By "app" I believe you are referring to the Member Tools app on mobile devices, right? Try using the Ward Directory and Map app on the church website (accessed through a web browser). Sometimes one tool is more successful than another.
Other thoughts:
- If you are under 18, you may need to have a parent do it.
- Try a different web browser
If that doesn't work, talk to your ward clerk or assistant clerk to see if he can help. They have access to Leader and Clerk Resources, which is yet another way to get your photo changed.
If all else fails, come back here and tell us what you've done and we will try to help. The whole photo mechanism periodically has problems.