What you need to overclock your laptop's GPU is first of all a laptop with a dedicated graphics card. Don't bother trying to overclock a laptop with an integrated graphics chip from Intel such as "Intel HD graphics", "GMA 4500mhd" or anything of that nature. Only dedicated chips from AMD or Nvidia are eligible for overclocking.
Different tools are at your disposal for overclocking, and it can (usually) all be done with software solutions. The exception is when the manufacturer has made the unfortunate choice of locking down the card in the BIOS to prevent overclocking. You can use most of the same tools for laptops as those you would use for overclocking a desktop graphics card. You have to keep in mind, however, that the space inside a laptop is restricted and a laptop GPU is likely to overheat faster than a full-size graphics card in a roomy desktop computer chassis.