From the playlist’s Actions tab, or the menu on its row in the list. It cannot be undone.
What it removes
The playlist, its order, its durations, its schedule, and its assignments.
What it does not remove
The content. Every item stays in your library and in any other playlist it belongs to. A playlist holds references, not files.
Anything on other screens. Screens that were not assigned this playlist are unaffected.
What happens on the screens
Screens assigned to it stop playing it on their next sync. If it was the only playlist they had, they have nothing to show and go blank, so check what else those screens are assigned before deleting.
Cached files stay on the devices until space is needed. See Where content lives.
Consider disabling instead
Disabling achieves the same visible result, keeps everything, and is reversible. Delete when you are certain the playlist will never be wanted again.