My own cable modem

I did some research and I bought a Netgear Nighthawk Cm1200 to replace Xfinitys modem, I can't afford them monthly rental costs.

My question is, do I just install the Netgear modem like Xfinitys modem... Do I need to contact Xfinity before install?

I want to make sure I'm getting the most up/down speeds as possible.