If you mean you want to stay with Spectrum but buy your own hardware, I'd check with Spectrum first (their website might have the instructions too). Normally there are HW requirements for the modem you get and they will need to send a service person out to set it up for you. They might have instructions for how you can do it yourself, but either way the new HW must be setup in their system to allow the new HW to login. Personally, I would buy a separate modem and wifi for performance, but that does get more complicated for the tech setup. I ended up turning off the wifi from my DSL modem (which I still rent from them) and connecting my own. When my kids came home from school, we were always lagging on 20 mbps DSL. I ended up using Google WIFI. It has a main WIFI hub that you plug direct into the DSL modem ethernet port and two satellite extensions (mesh network technically) that allow better reception around my house. That actually allowed 4 kids, wife and myself (often with streaming TV on) to work on 20 mbps. Then when COVID hit, I had to bump up to 30 mbps since zoom calls where a bit more bandwidth hogish. But you can also purchase a simpler single WIFI setup that you would plug direct into the modem and follow their setup instructions. Replacing the WIFI alone won't save you the money, but it might fix the lag. Do you know what WIFI version your modem supports (802.11x where x is b, g, n, or other letters)?