Honestly, you can't just go from 2.16GHz to 2.5GHz just because you want - otherwise, new processors wouldn't sell at all, everyone would just make their processor's speed increase. Overclocking is always available, however, it's a very delicate process that can seriously destroy a computer if it's not done correctly. To make it worse, overclocking is completely different for different processors and devices. There are also processor-specific programs for overclocking, so if you get an incompatible one, you also might mess something up.
Now, here's the thing; going from 2.2GHz to 2.5GHz would make so little difference to a human that it's almost not worth the effort. Only if you need
to get every last bit of performance out of your computer should you look into overclocking.
Though let's all cheer in joy! This has inspired me to create an overclocking guide!
Unfortunately, I still have my Avant Browser Guide to finish up, as well as another projekt - then I may come to this one. (sorry if you were hoping of a soon release