Search for and open record for the person you are tying to modify.
Once the selected record loads hover your mouse over the photo in the person heading.
Click the "camera" icon.
A photo dialog will open onscreen.
Select the photo to be uploaded.
It would be best for all photos to:
Be 800x600 (aspect ratio of 4:3),
Have a DPI up to 600,
Be less than 10 MB.
Once selected a preview will display.
Select Save.
NOTE: It would be best for all photos to be 800x600 (main thing is to ensure they have aspect ratio of 4:3 so as not to be cropped weird), have a DPI up to 600, and be less than 10 MB.