I can explain how to you but I honestly don't think it's smart overclocking any M series cards. If you feel it's really needed I would only do it whilst gaming(Guessing that's why.) and return it to normal afterwards. It's not something anyone would actually recommend you do.
Oh you're playing BF3 on a laptop? Doesn't sound too good. If you want to send me a PM with all your specs I will give you some info on the overclocking and a few other things to improve Performace for BF3
Before you overclock anything (CPU,GPU,Ram etc check on your cooling on the item) and your case cooling ... and if your considering pushing some limits (don't OC what you cant replace)
I would recommend a cooling pad for under your laptop if you plan on Overclocking just to add on. You can get cheap ones online for $5 which would do the job. But if you're willing to put a few more bucks into it, it's well worth it.
I agree with MTRich OCing a lappy ... unless its something like a ROCK Lappy is not the best of ideas as standard lappy components are not high power so don't lend them selves to OCing and your cooling or lack of it will be a pain.
Most Laptop components cannot be overclocked in the first place. I highly suggest agaisnt it due to overheating issues. Laptops hold alot of heat as it is, overclocking a component would possible kill the laptop or the component that is being overclocked.