Here's a more specific guide:
1. Locate the valve cover: This is a rectangular piece of metal covering the top of the engine. It's usually held in place by bolts or studs.
2. Look for a small, round, black or blue plastic valve: This valve is usually located on the valve cover near the front of the engine, close to where the spark plug wires run. It will be attached to a hose.
Note: It's important to consult your Subaru Impreza 2.5L engine's repair manual for the specific location of the PCV valve on your particular vehicle. The location may vary slightly depending on the specific engine model.