In January of this year I upgraded my computer with the i7 930 with a Ghz of only 2.5, but I have found that 2.5 Ghz doesn't seem to be enough to handle the power of FSX. I just wanted to know will I have to get a new motherboard to upgrade to a higher Ghz or is it just the CPU which I need to upgrade?

You should overclock your current processor before you decide to spend money on a higher clockspeed processor within the same family. Do you have a motherboard that allows for overclocking or is this a name-brand system that doesn't allow overclocking? Don't worry about the how-to, there's plenty of hand-holding to be had for that.