Is there a way to remove the warp in plywood?
Most corespondents are right in that the warp is caused by an imbalance of moisture. The problem has little or nothing to do with the type of store from which it was bought because even if it was absolutely flat in the store if you store it incorrectly when you get it home it will warp. This is especially true if you stand it upright anywhere near a radiator or other heat source.

What happens is the side nearest the heat source drys out too quickly causing the wood to shrink on that side resulting in a 'bow' or 'warp' 

Now the thing is to rebalance the moisture content. This is accomplished by wetting the CONCAVE side (hot water works best) then laying the board CONCAVE side down and applying weights to flatten the board. The 'wetted' side will expand as moisture is absorbed on that side and the board will flatten. Some people like to apply heat to the CONVEX side. This will certainly speed up the process but you have to be careful not to cause the warp to reverse. Check the process from time to time. As soon as the flatness you want is achieved store the board flat. It is usual to 'condition' newly purchased material for at least 48-hours in the environment in which it is going to be used, before cutting and fixing. Hope this makes sense.
Albatross