How to get a pool filter's pressure to drop?

Have a pool that had not been serviced in 2 years or so. Needless to say, it is a swamp. We were told to just shock it daily 10- 15 lbs. The problem is, they installed a new motor on the pump, and it is apparently running higher in pressure than max psi for filter.We were told to backwash, and did it, but the pressure did not change. Any help .... pleaaaaaaase!