If my teachers already sent their recommendations and the transcript was already sent electronically to a school, but I no longer want to apply to the school, how do I remove the transcripts/recommendations?
I don’t think there is a need to “remove” them. If you don’t submit an application, they won’t review them.
Make sure to remove the school from your list of schools on the Common Application (there’ll be an “X” button on the upper-left side of each school’s name IIRC,) so that you can use that spot for a different school if you so wish.