If you have imported objects into your drawing from DWG or Sketchup, and is no longer using them, you can clean up your drawing with Files > Purge... There you can select on a per object basis, or all unused
Alternately, if you are looking to remove Custom Library Items that you created yourself from within a file and which you made available to other files, you must do this from the WYSIWYG Welcome Screen, by browsing the Library from there (OPTIONS menu) and then right-clicking and deleting the objects one-by-one. This will cause those Custom Library Items not to appear in the Library for new files that you create, or in files that you open, in which you did not insert those objects; they will of course appear in files where you inserted them (or those where you created them) as they are part of the files' "private Library". Cheers, Dany
