Start by heading to Settings (the gear icon on the top right of the Home screen).

You then have to go to your Squad.

To add a photo of player, simply tap on one of the existing players in the list of players.

You now enter the Edit player state. At the top of the page, you will see a camera icon. Tap on this icon.

You now get to choose which photo you would like to use.

Click on a photo and press SAVE. 

Remember that it could take a while before the new photo appear in the Forza Football app.