The maximum dimensions are 150 x 150 (width x length).
If you try to add an avatar from a website which is larger than the above dimensions, then you're going to get a message which says that the avatar is too big. I think that's what happened to you. So, you have to find an image whose dimensions are equal to or less than 150 x 150.
But, if you upload an avatar from your computer, then the image will automatically resize to the maximum dimensions allowed for an avatar.
If you try to add an avatar from a website which is larger than the above dimensions, then you're going to get a message which says that the avatar is too big. I think that's what happened to you. So, you have to find an image whose dimensions are equal to or less than 150 x 150.
But, if you upload an avatar from your computer, then the image will automatically resize to the maximum dimensions allowed for an avatar.
