In settings where you can up-load the avatar it has a size limit in the box that pops up,

(85 X 85) Max. 7.5KB;
jpg/gif are supported

If the box is blank (white letters) Hold down the left mouse key and drag accross to highlight, should be able to read what it says.

If You can't resize the pic small enough up-load it here and I will try to resize it for you, If I can?

The auto re-size works in the forums, but not for avatar's