Well that CPU is a socket LGA 775. Based on just that information alone the following might be the CPU's you can upgrade to...
However!! A CPU that will actually work may not be any of these. It's all based on your motherboard. If you don't know what the make and model of your motherboard is then tell us what PC you have... like Dell Inspirion Ex550
Core 2 Quad Q9450
2.67 GHz 2 × 6 MB 1333 MT/s 8× 0.85–1.3625 V
95 W
LGA 775
Core 2 Quad Q9450S
2.67 GHz 2 × 6 MB 1333 MT/s 8× 0.85–1.3625 V
65 W
LGA 775
Core 2 Quad Q9550
2.83 GHz 2 × 6 MB 1333 MT/s 8.5× 0.85–1.3625 V
95 W
LGA 775
Core 2 Quad Q9550S
2.83 GHz 2 × 6 MB 1333 MT/s 8.5× 0.85–1.3625 V
65 W
LGA 775
Core 2 Quad Q9650
3 GHz 2 × 6 MB 1333 MT/s 9× 0.85–1.3625 V
95 W...