Well here is question about avatars usage -)
Tell me how to use it and I'll pull request a doc for it.
Go to 'Settings' -> 'Change User Details' and there you should find a input field called 'Avatar'
You can modify the allowed sizes (width/height/size in kb) in the admin panel.
For this, go to 'Management' -> 'Settings' -> 'Misc Settings' and scroll down to the avatar settings.
Cheers! 🍻