Except for Forester 2002 and older, you need to drain your cooling system, detach both radiator hose and bypass line from the pump, then detach both cooling radiator fans. You'll first remove the drive belt cover and then take the belts out of place. On engines without a turbo, first you need to take out the tensioner and idler pulley under the water pump, then two parts of the timing belt assembly from the left camshaft, and finally remove the cover from the back of the engine where timing belt runs. For cars with turbo engines, take off these three parts from both sides of the water pump: the timing belt tensioner and idler pulleys sitting just above and below pump, and the camshaft position sensor. You should remove all bolts from the water pump, get the pump and old gasket apart from the engine, and completely take off any residue from the old gasket while cleaning the surfaces. Make sure the replacement pump matches what you took off, put sealant on both sides of a fresh gasket, and place it on the pump. Spread RTV sealant on the threads of each mounting bolt, place the water pump gently, making sure it sits correctly with the gasket, then screw in the bolts without over-tightening. Start with the middle bolt on the right side of the bolts, tighten them clockwise, check the torque rate after, and complete all bolts following this pattern. To finish installing the water pump, you follow the same steps in reverse order: put back all the parts you took out for access, attach the hoses to the pump, use firm grip to turn your hose clamps tightly, top up your cooling system, and make sure your drivebelt is set correctly.