change a modem

My current modem is "N450 WiFi Cable Modem Router" and already used it for over 2 years

Since  I really have high quality requirements on the network. I'd like to change a better modem.

so my questions is :

1. is it possible for me to buy a modem by myself other than buy it from COX?

2. Is it possible for me to assamble the new modem by myself? (Is there any  iternal settings is necessary to be set by COX staff on-site?)    I have  ntwork setup experience, but not sure if COX machines need extra settings.