Most 120mm tower type coolers should be ok for at least a mid level overclock.
Make sure your case fits the cooler AND you have the power for it. Not all boards overclock as well(in general, the more beefy voltage system, the better) and every cpu is different so no one can guarantee a clock speed.
Now when overclocking these cpus you just increase the multiplayer and test(some use games, some prime or other stress tests.).
You keep going until you hit a wall(crash/errors) or get too hot(I do not think you want to see over 65-70c[lower the better] for the cpu, video cards can run up into the 80-90[some hotter] area without issues).
If you hit a wall and are not too hot adding a bit of voltage(go in small steps).
At some point you will hit a point that it takes lots of voltage and generates lots of heat to get any further. This should be the stopping point(even backing off a bit may be a good idea).
Keep an eye on the cpu clock speed as well because some systems will throttle under load. This can be from the board getting too hot(thus the beefy voltage regulators tend to be better statement). Many users add a fan over the VRM area(around the cpu you will see caps, coils and transistors[covered with a heatsink many times].). If you are using an aftermarket cooler using the stock coolers fan for this job works fairly well too.(a 90 degree bracket can hold the stock fan right over the VRM area by attaching it to the rear case fan.)
An example of how such a setup would work
It will be best to read some guides and your board manual to get to know what you are after. You can run a game benchmark before and after to judge if the improvement is work it to you or not. Some games are just not that cpu demanding and will not see much boost, while others love it.
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