Hi sweetandsalty568,
I understand you purchased a television series on the iTunes Store, and you want the next episode in the series to play automatically when you are watching it with your Apple TV (3rd or 4th gen). You can do this by creating a video playlist on your Mac computer, and then using Home Sharing to stream the content from your computer to the Apple TV. I'll include some resources below for iTunes and Home Sharing on your Mac. On your Apple TV, in the Settings menu, change "Show Playlists" to "All" (the default setting is for Music Only.)
iTunes 12 for Mac: Create a playlist
The examples in this resource are for music files, but you would select the video category instead of music.
Use Home Sharing to share iTunes content with other devices
Take care,