As long as your rpm is kept high you'll be able to reduce pressure and shift easily. But think ahead and watch the slope. If it's getting steeper you can see you'll need to be downshifting as your speed drops and your pedal rpm goes below about 40. Don't wait until your pedal rate is 10 rpm and then try to downshift (at that stage its best to get off the bike and walk or lift the back wheel up to shift).