Dell xps desktop has 3 sticks of ddr3 ram...windows 7 64 bit...what is best ram

[fleetopssupt]

Fairly new Dell XPS desktop with Wind 7..64bit..has 3 sticks of Ram (3gb total)..has 4 slots..what's the best way to upgradethis for a bit more ram/performance?

 

[nikorr]

The CPU is ?