How to stop using Time Capsule as router?
I have a Comcast router XB-6T and it's suppose to be better/faster than using my Time Capsule/802.11ac as a router.

Better/faster is very subjective.  You need to define what &quot;better&quot; and &quot;faster&quot; mean to you.  But for comparison:

Both are 802.11ac devices
Both have Gigabit WAN connection (the XB-6 claims &quot;a maximum&quot; of 1 GB throughput)
Both have Gigabit Ethernet ports.  Apple has 3, Xfinity has 2
Both have dual band (2.4GHz and 5GHz) radios

So, from a performance perspective, there's really nothing that stands out.

We do have Ethernet cables plugged into the back of the TC that goes to other rooms/devices and one USB on the back of the TC that goes to a printer.

Whether or not you have Ethernet cables plugged into the TC or the XB really doesn't matter.  The TC is plugged into the XB (it must be if you have Internet) then regardless of which device you plug into, they're all Gigabit, so there's no advantage to doing this.  The XB6 doesn't mention USB, so you'll want your TC to act as a print server.

I'd like to know if someone can give me instructions how to no longer use my TC as a router and instead use the Comcast router but also I'd like to keep the same Network Name

In order to configure your Airport Time Capsule, you need the Airport Utility and related documentation:

Airport Utility 6.3.1 for Mac
Airport Utility 5.6.1 for Windows
Airport Utility Users Guide

We don't know and cannot support your Xfiniti device.  If you want to use that device with the same name as your Time Capsule, you'll need to consult their support options.  That said, if you wish to use their WiFi, you have to make sure the WiFi on the TC is either

turned off; or...
set up in &quot;client mode&quot;.

There's detailed information on how to do this in this Support Document.  If this is not something you're good with and/or don't know how exactly you want it configured, I highly suggest getting a local tech person to come out and set this up. There's simply too many variables for a succinct answer in this medium.  Additionally, there's no way of knowing how the XB is configured to properly advise you how to configure the TC.
Bottom Line....
If WiFi on your TC is working fine, then there's no reason to change.  In other words, if you're satisfied with the performance, there's no need to do anything.  If you want to maximize the efficiency and coverage of your WiFi, you need to bring in someone familiar with this kind of work.