If yeh drop the resolution you play at it will reduce the lag considerably.
After that kill shadows, reduce yer view distance, those are the big ones.

On all the other wows take the graphics affects bar, the big one, and drag it all the way to the left.

The problem yer running into is not enough memory the higher the res yeh play at the more memory yeh need.
Alll those affect require a considerable amount of cpu cycles. WoW does most of the graphics on the cpu.