Click on user CP mate
you can see the option for EDIT AVATAR ON left hand side as shown click on it.
after you ill get the following:
there is an option uploading avatar from your pc, and make sure the avatar is 150x100 pixels.
you can resize any image to suit avatar size by Image resizer too you can download it here:
click here
after resizing the image you can upload the avatar to photobucket.com and copy the link and paste into Option 1 on EDIT AVATAR
HOPE THIS help.