I was trying to clean up my library also and moved some of my user items into the trash (scroll to the very bottom of the library browser to find trash). Once they were in the trash folder I hit the delete button on my keyboard....and poof! gone. I then selected several items in the trash folder at once with the shift button and then hit the delete button on the keyboard again...and again...poof! gone. You might be able to drag a whole library into the trash folder and then select it and hit the delete button. Good luck. I am back to working on cleaning up my library one item at a time.
I am looking for a CA licensed architect to help with plans for a home in the Ventura County area. Elaine