Are you having issues running FSX with this setup? If it runs it okay, you don't need to do anything!
If you are experiencing performance issues, you could get a new video card to replace both of them. Like a 750Ti, GTX760, or GTX770. Just double check your power supply to ensure it can handle a new card.
Something else to consider may be to upgrade the processor to a quad core Q6600 or similar. Can probably find one on eBay or in the for sale section on the forums.