How do I change my avatar or bio?
Both live under Settings → Profile — upload an image and write a short bio.
Go to Settings → Profile. You can upload a PNG or JPEG avatar (up to 2 MB, cropped to a square) and write a bio of up to 500 characters. Both save straight to your account and show on your public profile.
A few profile fields — display name, country and website — are shown as previews for now and aren't editable yet. They're clearly marked, and they'll switch on in a later update.