...by going into impulsedriven.net   Community......My Account.......  and accessing your account details from there....it allows you to upload 100x100 avatars,  max 40kb...jpeg or png....but...when I went to change to my Christmas avatar....found it's broken for the time being....for me anyway....so I'm back to shrunken... 
I can only get it to change via my old pc. I'm assuming it has to do with the version of Flash you have.