Windows 7 vs Windows 8:
First of all, I strongly recommend leaving things the way they are. GAMING is basically identical.
Aside from the new interface, and minor other things there's little difference.
RAM USAGE:
Probably said above but Windows is SUPPOSED to use most of that 4GB. It's called "intelligent buffering" so that the fast System RAM contains data you may need such as launching a particular program. If you start a game it can clear up space automatically so there's no issues.
With 4GB I've never seen a need on multiple computers to modify anything to make the PC run better.
SUMMARY:
*Long story short, I think it's a waste of money to "upgrade" to Windows 8 from Windows 7, and again GAMES will be basically identical.
There's a lot better ways to spend $100. For a laptop, that could mean replacing the HDD with an SSHD (Hybrid Drive) though I wouldn't bother myself.