Find your avatar above top right. Select Manage Now Account. Select Now Membership.
Now go through the indicated Cancel option you see there, for each Membership you wish to Cancel. Make sure you complete the multi-stage process, and get an email from Now, confirming the Cancel, for each Membership you Cancel.
If you don’t find any Memberships there, though, then you probably bought Now from a third party, and have to cancel through them:-