Unlock your iPhone
Press and hold the Lock Screen
Tap Customize
Tap Lock Screen
Tap the clock to change the font and color
Tap the date or widgets area to add or remove widgets
Tap the wallpaper area to choose a new photo, color, or collection
Tap Done
Tap Set as Wallpaper Pair if prompted
Go to Settings
Tap Wallpaper
Tap Add New Wallpaper
Select a wallpaper
Tap Add
Tap Set as Wallpaper Pair or Customize Home Screen if prompted