You first have to prepare an image that is 100px by 100px or less, using your preferred image editing software. Then you go to the "Edit Avatar" section of the "Profile" tab of the User Control Panel (upper left). Here's a direct link:
I have tryed a few time's already to add a pic to my profile and it keep's telling the same thing over and over no matter how small i make the pic can you help with this please
How small are you actually making the image? They need to be pretty small. (less than 100x100 pixels), but also less than a certain size file (which should be easy with a simple JPG or GIF).
Or even "this" site. I setup a simple (very simple) tool where people can upload a basic image and have it converted to appropriate sizes for the forums:
That topic (sticky in Website comments) has information and the link to the tool. It doesn't, however double check that the file size is within limits... only that the image dimensions are within limits.