If you're happy with your computer as it is, leave it alone. Lots of damage can be caused by unnecessary messing around with it.
If you really want to increase your RAM, go to the Crucial site click here and it will tell you what memory is suitable for you via a questionaire.
Overclocking is for those with suicidal tendencies only. If it goes wrong, it's dead.
If it ain't broke - - - - -