Hey Lesley - I wouldn't shout wherever you had put it!
You need the pic to be a max of 150 pixels wide, and 200 pixels high, and the file size cannot be more than 64 KB.
So I use this website to shrink pics http://www.shrinkpictures.com/
Click the create avatar option, then select your pic and put 150pixels
It will then ask you to download/save it - so maybe save to your desktop
Then on BANDA click on profile and then click Avatar - upload it from your computer and save
Voila!