From the File menu, select Compress Library (.enlx).
Specify the parameters for your compressed library (with or without file attachments; whole or partial library, etc).
Click Next and select the destination where you wish to save your compressed library.
Tip: Like searching for and discarding duplicates, regular backups of your library should be made (and stored in a safe location). These may be stored on a cloud-based drive, if needs be. However, you should move these files back to a hard drive on your computer, before attempting to open them and extract the compressed contents within.