Your iPhone stores a lot of information about your activities. Normally, this data is used to simplify the use of the device - for example by keeping track of websites visited or missed calls received. If you're concerned that someone might find out about you that you want to keep private, you can choose to clear the history of individual services on the iPhone or delete it entirely.
Steps
Method 1 of 7: Safari history

Step 1. Launch the Settings app
In order to delete the history of the websites you access, you must use the iOS "Settings" menu; in fact, it is not possible to do it directly from the Safari app. To be precise, from the Safari application, you will be able to delete the data relating to the history of your browsing, but you will not be able to delete the data relating to automatic compilation or cookies. On the contrary, deleting the history directly from the "Settings" menu will guarantee you the total elimination of all sensitive data stored by the browser.

Step 2. Scroll through the list until you find and select "Safari"
It should be within the fifth group of menu options.

Step 3. Scroll through the "Safari" submenu to locate and select the "Clear Website and History Data" button
A popup window will appear asking you to confirm your action.
If the "Clear website and history data" button is grayed out (grayed out), you need to disable access restrictions. Return to the "Settings" menu, then select the "Restrictions" item. Type in your access code, then tap "Websites". At this point, to enable the deletion of the history, select the item "All websites". If you do not have the access code to the "Restrictions" section of the menu, you cannot proceed with deleting the history

Step 4. Confirm your willingness to clear the history
Data regarding your Safari web history, cache, autofill and cookies will be deleted from the device. Also, the history information will be deleted from any other device connected to your iCloud account.
Method 2 of 7: Chrome history

Step 1. Launch the Chrome app
If you use the Chrome internet browser to browse the web from your iPhone, you can delete your sensitive information directly from the related application.

Step 2. Press the "Menu" button (⋮), then select the "Settings" item
In order to locate this option, you may need to scroll down the list.

Step 3. Tap the "Privacy" option
A new menu will appear giving you a number of options for clearing various information.

Step 4. To clear the history, press the "Clear Browsing History" button
In order to proceed, you will be asked to confirm your action.

Step 5. To delete all data regarding your history, press the "Clear All" button
This will delete all information relating to your history, cache, website data and cookies.

Step 6. If you want to delete the autofill information, click the "Clear Autofill Data from Saved Forms" button
This will delete all the data that is automatically proposed to you when you type something in a text field on a web page.
Method 3 of 7: Call Log

Step 1. Launch the Phone app
To prevent anyone from learning about the calls you make or receive, you can clear the data in the recent call log.

Step 2. Go to the "Recent" tab
It lists all the latest calls made or received.

Step 3. Press the "Edit" button located in the upper right corner of the screen
Red buttons marked with a "-" will appear next to each entry in the call log.

Step 4. To delete a single call log entry, press its red "-" button
This will remove the selected item from the list.

Step 5. To delete all the calls in the log at the same time, press the "Delete" button
If you want to completely empty the call log, press the "Clear" button located in the upper left corner of the screen. This button appears only after pressing the "Edit" button. This way all the entries in the "Recent" tab will be deleted.
Method 4 of 7: iMessage History

Step 1. Launch the Messages application
It allows you to delete messages related to any conversation.

Step 2. Press the "Edit" button
It is located in the upper left corner of the screen.

Step 3. Select each of the conversations you want to delete
To do this, press the check button next to each conversation you want to delete. You can also select multiple items from the list.

Step 4. Once your selection is complete, press the "Delete" button
All selected conversations will be deleted immediately, without you being prompted to confirm your action.

Step 5. Change your message history settings
By default the Messages app stores all your messages indefinitely. You can change this mode of operation so that your text messages are stored for years or only for 30 days, freeing up memory space and optimizing the organization:
- Launch the Settings app;
- Select the item "Messages";
- Tap the "Keep messages" option;
- Select the length of time you want your messages to remain stored on the device. After the chosen time interval has elapsed, the messages will be deleted automatically.
Method 5 of 7: Reset the Keyboard Dictionary

Step 1. Launch the Settings app
If you want to delete the words that you have entered in the vocabulary of your iPhone, you can do it through the Settings application.

Step 2. Select the "General" option
The list of items in the "General" menu of your iPhone will be displayed.

Step 3. Scroll through the list to locate and select the "Restore" item
You will be presented with several options for restoring the basic settings of the device.

Step 4. Press the "Reset Keyboard Dictionary" button
You will be asked to confirm your action, after which all words that have been added to the vocabulary of the device will be deleted.
Method 6 of 7: Clear Google Search History

Step 1. Launch the Google app
If you normally use the Google application to search the web, you can also use it to clear the history of all searches you have performed in the past.

Step 2. Press the gear button in the upper left corner of the screen
The "Settings" menu will be displayed.

Step 3. Scroll through the list to select "Privacy"
Your active account will be displayed.

Step 4. Tap "Navigation"
The "History" section will appear at the top of the screen.

Step 5. To delete your search history, press the "Clear History on Device" button
Note that this action only clears the search history for the application you use on your device. Your search history will still be present on your Google account.
Method 7 of 7: Erasing All Data

Step 1. Use this procedure if you want to delete all data on your iPhone
By following these instructions, all personal information stored on your device will be erased and, when finished, you will have to do the initial setup again, exactly as you did the first time you turned it on.

Step 2. Launch the Settings app
If you are sure you want to delete all data on your iPhone, go to the Settings app.

Step 3. Select the "General" item
Your iPhone's "General" menu will appear.

Step 4. Scroll through the list to locate and select the "Restore" item
You will be presented with several options for restoring the basic settings of the device.

Step 5. Tap "Initialize Content and Settings"
You will be asked to confirm your action.

Step 6. Wait for your iPhone recovery process to complete
This may take some time.

Step 7. Set up your iPhone again
Once the reset is complete, you will be guided through the initial setup procedure. At this point you can choose to configure your iPhone as if it were new or to restore the configuration using an iTunes or iCloud backup.