For overclocking, we always need more details.
What motherboard ?
What Ram ?
In short, with stock fan, you can bump it up to 3.4 and probably 3.5 easy... just go to the Bios and bump up the cpu multiplier.
Go to google, search, download and install hwmonitor
google, prime95 and install it.
Run hwmonitor, run prime95 and monitor your temps and system stability.
You are safe and rock solid as long as under heavy load you do not go higher then 61 degrees... if you do I recommend a better cpu cooler.
With a good aftermarket cooler, you can go higher and if the system crashed, bump up the voltage a bit, in hwmonitor you will see where it's at... Do not pass 1.48.