Dino,
There's no reason to pay big bucks for something like Photoshop if you're an occasional user. If you're on a Mac, I highly recommend
GraphicConverter.
Whatever your software, you need to do two things. First, you need to shrink your avatar image to 140x140 pixels. Second, when you save your avatar file you should apply a fair amount of JPEG compression so the file size will be less than 20K bytes.
Enjoy!
-- Jim