Unfortunately even if you cancel both your existing entertainment & cinema passes on your account you still won't be eligible for the Christmas 12 month combined entertainment & cinema offer.
I you are desperate to take up this offer you could try live chat and tell them what you are after.
I know during the Black Friday offer, live chat was prepared to wipe customers existing passes on their account (which you would forfeit & lose) where customers was then able to purchase the new 12 month offer.
Not saying that live chat will be prepared to do this on this particular Christmas offer, where the Black Friday Sales may have been a one off due to the amount of flak & pressure nowtv was getting during the Black Friday promotion offer from customers.
If nowtv live chat are prepared to do this for you then you need to weigh up the option of losing your existing current passes on your account.
Otherwise i don't normally recommend this, but cancel your passes and create a new account to take up this Christmas offer.
To reach live chat open the link below and click on the small blue arrow directly underneath How to Get in Touch to reveal the live chat button to click on.