How do I switch my internet equipment?

Thanks for the helpful link on how to return! 

I've already scoped out some equipment, I was more so wondering how I would change my plan to reflect that I'm no longer renting the equipment. Would I just choose a new plan from https://www.xfinity.com/digital/offers/plan-builder?

You are very welcome, and that is correct, user_gvqfjx. You can elect to use an Xfinity Gateway or your own equipment, and this helpful link has step by step instructions on how you can activate your own equipment using the Xfinity app.

Activate an Xfinity Gateway or third-party modem with the Xfinity app

Awesome, one more semi-related question: I was going through the plan change process and noticed that there's no current option to keep my "Blast! Internet Plan" (800 mbps download, $90 after temporary discount), so it doesn't look like I'll be able to remove the rental without having to change my plan.

The best plan for me of the new ones would probably be 500 mbps at $105, which is the same monthly cost as my current plan plus the rental ($90 + $15) while also decreasing my speed. Is there any way to keep my current plan while removing the rental?

That is not necessarily so @user_gvqfjx.  You can return the device in a local Xfinity Store and they can have it removed for you.  Have you already purchased the new device?  We can assist with activation and removal of the fee as well.