You can edit your profile picture via your avatar (top right-hand corner) > Personal settings:
You can remove your current profile picture by uploading a new picture:
If you've uploaded a picture once, you can't go back to the default avatar, so you can upload a blank image to remove your current picture.
Need a hand? Contact our friendly Support team via the in-app chat at the bottom-right of your screen, or email email@example.com.