The following steps should get you there or at least very close:
1. Go to the directory web app:
https://directory.churchofjesuschrist.org/
2. Find your entry in the directory;
3. For individual photo, click on your own name;
4. Click on the blue circle with a drawing a pencil;
5. Click on 'Photo';
6. Click on 'Add Photo' or similar;
7. Follow the prompts from there.
You might also be able to change your photo on one of the apps, but I don't have a way to check that for you.