Upgradeability depends on what's in the system now. They were shipped with up to an i7 2630QM CPU. You're limited to the second-generation Core i CPUs, and if you upgrade from an i5 or lower to an i7, you may need a new AC adapter as well (you'll need 130W or better depending on the GPU in the system, where the i5 will work with a 90W or lower adapter).
You likely have an Intel GPU (that cannot be upgraded without replacing the mainboard). You will need a 90W adapter to upgrade to an i5 and a 130W to go to an i7.