Each line has an end contract date. Check the device on your My Verizon web portal. If its out of contract then a simple port out to another provider will remove that line. However if the account belongs to you then its you that must go and give the new provider your verizon wireless account number and pass code. I doubt another on your plan could iniate the port on their own.
Otherwise you would have an early termination fee for the line if the contract had not ended.
If one of your other phones is out of contract you can transfer the upgrade and port the phone out. In order to keep the phone number the new account has to be set up first, with the phone number.
I tried to pull this off online, but no go, it switches the upgrade back unless you buy another phone. You will have to go in to a store to get it done.
Otherwise, be prepared to pay the ETF.