I've noticed that every update is 5.50 mb. Does that mean each update takes up 5.5 mb space on my hard disk or is it overwriting the previous update?

You'd be better off posting that question on the Malwarebytes forum I would have thought: http://forums.malwarebytes.org/

It over-writes it.

If you want to take a look, navigate to: C:\ProgramData\Malwarebytes\Malwarebytes' Anti-Malware\

Cool, that's what I thought, just wanted to make sure. Didn't feel like cruising over to the MWB site. Initial google search didn't reveal anything either. Guess there aren't too many people still using computers from 2000 with less than 20 gb hard discs (and thus need to be stingy about memory).