Amit, i know it just shows up as Radeon 5 series in your windows config so if you could take the side of the computer off and find out exactly what graphics card it is, the guys above will be able to help you.
metro 2033 is a very demanding game, if you are trying to play with dx 11 it will laggy no matter what videocard you have try removing DX11 DOF, and lower graphics settings this should fix your lag.