How do i delete an app from my 3rd geeneration apple tv

You cannot delete channels, however you can hide them. Also, they are not apps, as Apple TV 3's did not have an app store.

Please follow the instructions to hide a channel:

To hide a channel, select it and then press and hold the center button on the Apple TV remote. The icons should begin to jiggle--just like on iOS. To hide it, press the Play/Pause button. A dialog box will appear asking if you want to hide the channel.