That's how it's done:

Here are steps to change wallpaper on Android device:

1. Open the Settings app on your Android device.

2. Select "Wallpaper" from the options presented.

3. You can now click on "Gallery" to select the image from your gallery. It is also possible to select up to 15 wallpapers on Android devices. Each time you unlock your phone, one of the selected images will be your wallpaper.

4. You can now choose where you want the selected image to appear as the wallpaper. Click Home Screen, Lock Screen, or Both to choose the settings you want.

5. Adjust the image by moving and zooming until it looks the way you want.

6. Click "Save" or "Apply" to apply the selected wallpaper to your Android device.

That's it! Now you have successfully changed the wallpaper on your Android device.