This article teaches how to change the lock screen wallpaper on Android.
Steps
Step 1. Open the "Gallery" application on your device
You'll find it on the Home screen or in the app drawer. The icon depicts a painting or photograph, while for Samsung users it is orange and features a white flower.
Step 2. Tap the image you want to use
It will open in full screen.
Step 3. Tap ⁝
This button is located in the upper right corner of the screen. You may need to tap the screen once in order for this button to appear. On some models there are three vertical lines instead of dots ☰.
Step 4. Tap Set as Wallpaper
This option may also be called "Set lock screen", "Set photo as" or "Use as", depending on the device.
Step 5. Tap Lock Screen
The name of this option can vary.
Step 6. Edit the photo in the box
Only the part of the photo that appears in the box will be used as a lock screen.
Step 7. Tap Save or Done.
This option may be called "Set" or "Set Wallpaper" on some models. This final step will change the background of the lock screen thus making the selected image appear.