Settings -> Personal Settings -> Change name/picture of your room.
There you will have two options: a) upload avatar b) make a selfie -> click on Update and you are set!
To keep the platform as authentic and real-time as possible, we recommend taking a live image through your camera. If you don't like the picture you took the first time, you can update it.
If you don't have a camera connected to your device, there you can upload an avatar/profile image instead. To make sure it's not distorted the photo should be square.