I would overlclock it in the BIOS settings, when the computer boots up. But unfortunately most Dell computers don't allow you to overclock. I you can't do it in BIOS, you can't do it. (Hold DEL while the computer is booting to go into setup, or maybe some other key with Dell laptop.)
Why would you OC it? Laptop CPU's can't be OC'd even if they could you put your CPU at risk of frying and perhaps even breaking other hardware. Plus, laptops have bad airflow (as you said cooling issues) heat is a big thing after OCing.... Even at stock, laptops become insanely hot underload (or 100%) I know because folding on my laptop (Intel P8700), it'll run extremely hot after even an hour of folding. All in all like zipzoomflyhigh said, you don't OC laptops.
I'm currently folding on my Dell Latitude D630 (it's been running for 7 hours right now) (CPU: Core 2 Duo T7250 @ 2GHz) and it isn't running hot. But yeah, the airflow of a laptop definitely isn't conducive to Overclocking. It would be a cool concept to explore though.
I have a D630 ATG and i cannot seem to find the settings to do it. maybe you can flash a custom bios or something but i will not be a good idea. my freind overclocked his HP and it fried the entire thing.