If you still have internet and TV service through Comcast you can not cancel your account. However, if you just want to change it, you can open a secondary account and make that one primary.
If you have cancelled your TV and internet package you can then ask Comcast to delete your email account. It usually remains open for 90 days and is then closed and the address is put back into the pool for other users.
If you want your email account deleted before the 90 day period, you can call 1-800 comcast and they will do that for you.
If you do decide to open a secondary account and make that one primary, you can then delete the other account (your main one at the moment) without a problem. You can also have your Comcast email forwarded to another address (gmail, yahoo etc) if that makes life easier.
