How do I delete TV show rentals from my iPod touch after watching them?

I'm sure I'm missing something obvious, but I've downloaded and watched a bunch of TV episode rentals. After they've expired (48 hours after I begin to watch) they're still on my iPod Touch (4th gen) and iTunes (10). How do I get rid of them? They're not deleting themselves automatically from either my iPod Touch or my computer. Help! Thanks!