question about sky subscription

fenster

Since longer time I'm thinking about getting such subscription, although the charges of these "resellers" are almost beyond good and evil.
So if you once a subscriber to sky, your contract will count for one year and after 1st month you can make changes to add/remove packages but how is that working f.i. I start with variety + movie package my subcription, did I need to stay for one year with these combo or can I cancel movie package after 1 month and add sport instead or downgrade to variety only ?

Thanks for assistance