You can delete an EndNote library in one of two ways.
One option is to exit EndNote and delete the library file and its associated .DATA folder by dragging the icons to the Recycle Bin on the Windows desktop.
To delete a library from within EndNote:
Close the library, but keep EndNote open.
From the File menu, select Open and then Open Library.
In the file dialog, highlight the libraryname.enl file, right-click your mouse, and click Delete.
Next, highlight the libraryname.DATA folder, right-click your mouse, and click Delete.
Click Cancel to close the file dialog.
Exit EndNote and delete the library file and its associated .DATA folder by dragging the icons to the Trash in the Macintosh Finder.