Solved
Roku setup on a tv that already has another user
How can I add my account to a tv someone gave me that already has an existing account?
The only way to change the user account on a Roku is to do a factory reset and set the device up from the beginning. This will remove all installed channels (and any associated login information) and will be for all practical purposes a brand new device. As long as you can still access the menus with the remote, you can easily do a factory reset from the Settings/System menu.
