If you are the "group creator", you should have administrative rights (I don't). But if you right click on the picture, it will give you the choice of "save picture as". Save it to your files, then at the right top of the group home screen, the administrator will have "change image" or something like that. From there you can upload the file. I'll look to see exactly what is said there to see if I can help you. Let me go to a group I created and see.