If you know the exact brand name and specification of your motherboard, there might be a slight chance, that there are newest/latest BIOS-updates and mainboard chipset drivers available, which, for instance, could allow the use of a faster CPU, which still would fit on the mainboard's CPU-slot, or maybe could open the barrier of 1 GB RAM sticks to use larger RAM sticks to get more of 4 GB Ram.

To run through a BIOS-flash process is basically an easy task if you're used to do those things, but on the other hand, if you mess up one step during this process, it could damage your existing BIOS and the PC wouldn't run no more ...
So this is only something for an experienced hardware user, not for someone with only basic knowledge in the hardware area ...