Hey there, welcome to Blahtherapy! It's nice to have you here :)
I haven't been here long either, so I know this place is confusing at first.
First of all, the Q-N-A section is for people who want advice or have problems. Site issues should probably be posted under Groups>General>Forums :)
Secondly, to answer your question, you should click on your profile name, then on the horizontal bar that reads "Activity Profile Messages..." go to Profile. Under the colorful main window there's a horizontal menu that reads Public, Edit, Change Avatar :) Go to the Change Avatar and upload your image! Make sure it's a small file (if it's too big it won't know how to resize it) and that the file extension is a JPEG, GIF or PNG. I hope this helps! If you have other curiosities about how things work around here, feel free to message me, I can probably answer, or direct you to someone who knows :)
