If your D.E. filter is leaking from the seam where the two halves of your filter meet then you may have a bad filter body O-ring. Another sign may be that you hear a gurgling or sucking sound from the filter. This is a moderately easy fix and this guide will take you step by step through replacing it. Some steps may vary depending on your filter make and model.
Now that your water is no longer circulating through your filter system, switch your valve to the "Closed" position. When changing your valve setting be sure to always turn the lever in the same direction. By using clockwise and counter clockwise turns of the lever you may cause unseating of the valve key gasket. This unseating may cause leakage from your waste port.
Again, loosen these with pliers until the metal flange can jiggle. it would be best not to remove these bolts completely as they can be hard to reassemble.
After tamping the entire circumference once or twice you should be able to lift the top half off by using the handles of the filter.