There is a post on here that tells you how to remove the scroll ball, but you need to pop off the chrome looking rim (sometimes finger nails will do) then turn the phone upside down and shake with your hand underneath to catch the scrollball assembly when it fall out.
The dirt build up on the black rollers is what causes it to stick. Clean it off then put it back in, along with the rim and it should be good
Posted from my CrackBerry at wapforums.crackberry.com
I just dampen the q-tip(do not have it too wet) and just brace the trackball on on one side with my finger and rub the part that is available. It just keep rotating it around.