Converting an octalink bottom bracket and crankset to a fsa bottom bracket and compact crankset 9 speed
My current favorite reference on the mess that is bottom bracket compatibility is this BikeRadar article. 

To summarize the BikeRadar article:
"Conventional Threaded: Standard 24mm external type (Shimano Hollowtech II [, Shimano Octalink], SRAM/Truvativ GXP, Campagnolo Ultra-Torque, FSA MegaExo, Race Face X-Type,  etc), square taper, ISIS, BB386 EVO" can all be put into the same frame. 

To do the crankset swap, you'll need to put in the MegaExo bottom bracket and then install the FSA crankset (you can't just stick a MegaExo crankset into an octalink bb) [This will require things like adjusting the FD as well, but you'll likely be using your LBS to do this swap anyway, and they should take care of it]. Note that you may also want to get a bigger rear cassette to help with hills (this alone may be sufficient and significantly cheaper), or even switch to a bike with a triple (and less race-y). 

Note that if you don't want to swap to a MegaExo BB, Shimano's Claris 2450 Crankset is an octalink crankset. And you may be able to take your current crankset and do some chainring swapping as well to get the desired effect.