When you choose to publish a loop in your school’s library, a copy will be made of the loop. Later, if you want to update your published loop, you just republish it again to the same library and your published loop will be updated with the changes you have made. When you want to publish your loop you go the loop under My loops, choose edit mode of the loop and click the name of the loop. At the bottom of the Start panel you will see Publish to library. Click that button and then choose to publish in your organisation library. In your organisation’s library you can publish your own loops, but also loops you have Remixed (taken a copy of) in a library.
