Due to retention concerns, you cannot downgrade your package without calling Now TV.
However you can quite easily upgrade via a few clicks. Therefore downgrading is in theory as possible through the website as upgrading - it's only retention policy that blocks this and expects you to call instead.
As the phone line is now almost unmanned due to coronavirus, it is therefore impossible to downgrade your package. I've referred this to Ofcom. In the event that anyone from NOW TV reading this, can you not make downgrades available without need to call for retention purposes?