To delete a lookbook go to your Build page and select the check box of the lookbook(s) you'd like to get rid of. Click the Move to Trash button.
Lookbooks that are moved to the trash will not appear under the All tab and won't appear in search results, but can always be recovered.
To recover a lookbook, select the by In Trash filter and check the True box.
Click on the lookbook you would like to recover. Select the Move from Trash button to put it back in your main lookbook gallery.