You can easily edit titles from your library. The easiest way is to log into the Teacher Dashboard from any desktop browser (enter your Classroom password first, then your Teacher password) From your Teacher Dashboard, select Library from the lefthand menu, then click the small wheel/cog to the left of the title you wish to edit. Select "edit" from the drop down menu and you will be able to edit all the info for that title.
Type in any changes you wish to make or select genre, fiction/nonfiction, etc from their respective drop-down lists and be sure to click save.
The easiest way to delete titles from your library is from your Teacher Dashboard, select Library from the lefthand menu, then check the boxes to the left of the titles you wish to delete (if you wish to delete everything, select the box at the top left that will check all your titles) Then select Delete from the options at the top of that column.
Additionally, if there are multiple copies of the same book and you want to just add or delete duplicates, select "Book Copies, Locations, and Conditions" at the top of the page and you can add or delete copies on the far right next to each existing title.