Before you begin to clean your trackball, make sure to have clean hands, because any dust, dirt, or oil present on your hands may render the trackball useless.This process is the same for many different BlackBerry phone models, including the 8100, 8300 and 8800 models. If your phone is under warranty, be careful when disassembling the phone because it may void it.
Quick Solution
According to the official BlackBerry Support Page the quickest and least involved solution is to rapidly roll your trackball from left to right, right to left and up and down. This will often release any debris that is stuck on the trackball and allow your device to work properly again. While BlackBerry doesn't suggest fixing unresolved trackball issues on your own if you're adventurous and you balk at warranty issues you can also try the steps below.
Removing the Trackball
First, use a small Phillips head screw driver—not a knife or anything sharp because you risk damaging the phone; to remove the small plastic ring from around the trackball. Once you have taken the ring off, you should see three small prongs, on the left, the right, and the bottom. Put the ring in a safe place over to the side by simply pulling it off the device.
The trackball is then held in with a magnet, so it shouldn't take much force to get it out. Turn the phone over and let the trackball pop out. If you need to, give it a push, but not too hard.