How do you increase water pressure on a swimming pool filter?

Is this pressure of water going in a filter or pressure of water coming out a filter? Do you mean increase the flow of water? An increase in the filter pressure alone without going to a larger size impeller or newer pump will only indicate that the filter is getting dirty. If you need more flow consider changing the impeller or even upgrading the pump BUT you have to know what the outcome of that change will be. You have to know what the hydraulics and pump curve is in order to keep from overpumping the water. Too much flow can be detremental to the plumbing, the pump, the heater. Going to a large size pump most likely now increase your flow if the pipes can not handle that extra flow of water. Sometimes whrn a pump is not sized properly - going to a smaller size pump or impeller - whichever the case may be - will increase the flow of water or GPM. There is a is a trick or formula for sizing pool pumps, filters and heaters to a particular pool.