|"My son has a gaming pc (Was specifically built for his gaming needs)"|
Who built it, FUJITSU? It's not a very good configuration. The CPU is weak, the graphics card is weak, & because it's running Windows 32-bit, only 3GB out of the 4GB RAM is useable. The only thing that "sort of" makes it a gaming PC is the graphics card. The GT 240 isn't a great card though, especially if the one you have uses DDR3 memory rather than GDDR5 memory.
There's no point getting more system memory unless you plan on replacing Win7 32-bit with Win7 64-bit. A CPU upgrade is a possibility but without knowing which system you have, it's impossible to know which CPUs are supported.
NOTE: I've editted my response after finding the motherboard specs: D2812-A2 specs
Here's one possibility for a CPU upgrade: http://www.geeks.com/details.asp?in...
To upgrade the graphics card, the power supply needs to be taken into account. Generally, the higher the cards performace, the higher it's power requirements. If your system only has a 250W power supply, you will either have to choose a gaming card that requires low power or you'll have to upgrade the power supply along with the graphics card. Also, if the tower is a "slim style", the selections cards & power supplied will be very limited.
We need to know the exact model number of the system to be able to give more accurate advice.