Hd7850 his i7 3770 ivy low fps Help

hi i have recently bought a gaming pc but im having problems playing any newer game on high or very high i get alot of fps loss. on average on metro 2033 on high my fps will constantly skip inbetween 20-30 same with far cry and day z
when i play far cry 3 i can set some settings on high and some textures on low to be able to play but i also have to wait for the fps to pick up because when i start playing it it will lag up and loss fps realy bad

MY PC SPECS

i7 3770 ivy
his hd7850 2gb
16gb 1600mhz ram
650w power supply
1tb hardrive
asus p8h77-m le mother board

i have had the graphics card replaced and ram

please help me


i realy wana play my games on ultra or very high