Older trackball mice use rollers and mechanical insides and over several years the ball can get slow and sticky. Luckily you can restore proper function to your mouse through these steps.
The mouse I will be using for this is a Microsoft Intellimouse Trackball from 1998. This tutorial will work for any other trackball mouse that is made before ~2004. Most made after that don't use the same sort of mechanism.
Step 1: Find and Turn Retainer Ring
When you look at the top of the mouse were the ball is, you will see a ring surrounding the ball. This ring is what keeps the mouse from falling out when you turn it.
You can see a small notch or dot on the ring and one that lines up with it on the body.
Turn the ring counter-clockwise as far as it will turn. The notch on the ring will then be about 30-90 degrees from the notch on the body.