If you want to update your published loop, you publish your original loop again. The loop you published in the library will then be updated with the changes you have made in the original loop. Go to 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 in which library to publish your loop. If your loop is already published in the selected library, you will see that it is already published and an update will be made.