Just use the delete button in the application. The software will look after all the rest.
As already reported, once you buy a show you own it, it will not reappear in your calander (for subscription) and ALL the BUY buttons on the web and in the application will not be available. If you want it back in the future you can download it again.
Also: If you have slow/limited/expensive bandwidth, you can ***** the files to CD, DVD, external HDD, memory stick etc. and put them back later. But you are still best to use the application to delete the card when you have backed it up.