You can cancel your Sky TV subscription as long as you're not in a long term contract with them. Without a subscription your Sky Glass will still work as a TV https://www.sky.com/help/articles/sky-glass-without-a-subscription
You may be able to cancel on MySky, else you'll be able to phone them up.
If you're in an existing long term contract you'll need to wait until the end of your contract period.
