Q: How to manage the size of a full season of a tv show?

You can delete the episodes in the Videos app - select TV Programmes and the the series, and on the episode selection screen swipe from right-to-left across an episode and it should get a Delete button on it. Or if you want to delete all episodes tap the Edit button on the first screen (i.e. the main TV Programmes screen). You can also do it via Settings > General > Videos (under the 'Storage' heading) - that also allows you to delete an entire programme or individual episodes.

TV programmes can't be redownloaded in all countries, and even where they can be there is no guarantee that they will remain in the store for future redownloading - so before deleting them you may want to connect the iPad to your computer's iTunes and do File > Devices > Transfer Purchases so that you can take a backup copy of them.