Next inspect the pipes leading to the tap. If it's rigid pipework (not flexi) you will need to be super careful not to let the tap body move when you remove the cartridge as if it does it may cause the connection to leak. If flexi pipes (braided) are used it's a little less of a problem if the body moves a tiny bit.

Remove the cartridge using a 17mm ring spanner. Often cartridges are very tight & using an adjustable or open ended spanner does NOT give enough purchase to break it free without damaging the hex. Short sharp shocks work well too so personally (as I'm very experienced) I use an impact driver with a deep socket to 'shock' it free.