It relativily easy
I've changed it a couple of times on my C30. I found the tuffest part of the job was contorting my body to get at the screws that hold the pump cover on. The job is very straight forward, take the screws off and pull the old impeller out. Before you pull the old one off take note of which way the flippers on the impeller are bent. This will tell you the direction the pump turns and the way you want to bend the filppers on the new impeller when you install it. Sometimes the old one will not come out that easy. I've had to use a needle nose plyers and grab a flipper and pull. This will usually destroy the old impller in the process. If your worried about the shaft, use something like a screw driver to hold it in place as you pull. Make sure to only use the gasket that comes with the impeller. The gasket thickness is important!
