Why does rollerball on the mouse not scroll screen UP?

Greetings!

The mouse ball on the mouse scrolls DOWN easily but won't scroll up. Is there anyway to open the mouse to clean it? Does the ball on the mouse need to be rough on the surface?

I have tried cleaning it (mouse held upside down, using the iKlean expensive stuff) which worked for a while but now, no dice.

I am pretty handy and would love to have a way to fix this myself. Thanks so much.