Adding your team logos makes your website and the app look even better. If you want to upload the logos for your teams:
Go to the 'Season' tab at the top
Select Teams > Teams from the top menu
Click on a team name and under the 'Details' tab of that page you can upload their logo
The team logos will appear in the app for your players, on your website, gameday matchup and summary pages, and anywhere else your teams appear!