First enter bios probably by pressing delete multiple times when your computer first boots
Once it bios look around and try to find The menu for Frequencies. here you should find your cpu clock.
move this number up 10.
save changes by going to the last tab above or go to main menu and selecting save changes.
This will save your changes and reboot the computer. Once booted you can either try this porcces again or stay with that speed. don't overclock too high. I would reccomend only 40 clicks max for a n00b on your cpu speed in the bios.
10 install prime95
20 install realtemp
30 increase FSB
40 test with prime95 and watch temps
50 if no errors + temps < 70 THEN GOTO 30
60 if errors and temps < 70 THEN increase VCore and GOTO 40
70 if temps > 70 decrease FSB and END
80 if PC wont boot, clear CMOS, decrease FSB, GOTO tomshardware ASK AGAIN
We type overclocking basics so often, I'm entitled to have fun with it.
Recommend you read the Core2 Overclocking guide. It's basically the same thing only it gives you much more detail on how overclocking works.
Don't expect big results first time. What options you have and if its possible is entirely up to the BIOS your computer has Good luck, any specific questions ask away, 'how do I overclock' is too big a topic to answer easily, tonnes of guides on here and the interwebs in general