New xFi Gateway Activation

I got an updated gateway today. Rented. My understanding is that I can use my Xfinity app to activate this new device to replace my "old" rented modem. The card in the box states to "disconnect any internet equipment currently in use." Should I disconnect/unplug my old modem before using the app? Hopefully, the app instructions will be easy to follow. I'm not tech savvy and need all the help I can get.