That's how it's done:

Here are steps to change the wallpaper on an iPhone (iOS device):

1. Go to "Settings" on your iPhone.

2. Select "Background Image".

3. Tap on "Choose new background".

4. Choose your background image from your camera roll.

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

6. Tap on "Set as wallpaper".

7. Choose whether you want to use the image as wallpaper for your lock screen, your home screen, or both.

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