beaglejohn Trying to simply change the plan via the website when logged in won’t work.why not?
For various reasons (most likely revenue related) Comcast makes it hard to change a plan online which is not an upgrade (you can up your Internet tier, or change to a higher TV tier, online). If you want to side-grade or downgrade, you need to walk into a store, chat, call, etc.
In some states you have the same rights to cancel online as to order online, but changes are not required to not require communicating with someone who will try to up-sell (or side-sell) you. Cancelling and then reordering might (in some cases) get you a new subscriber offering, at a cheaper price, but you would lose any years of service bonuses.
Personally, I find it easier to walk into a store, but that is probably because it is less than 15 minutes away if I walk (given traffic, parking, etc. it is probably 10 minutes to drive, so the getting outside, and walking, would probably make my Doctor happier, should I ask them).