@
Smokva - you
cannot rename the current library, and rename is not available if there is only one library, so:
- switch to Calibre-Library and use the Rename option to change Calibre Library to Junk Library
- switch to Junk Library and Rename Calibre-Library to Calibre Library
- switch to Calibre Library and Remove Junk Library
Curious: why are you insisting your 'new' library use the default name. Should you ever need to do this again, you will have to do the same soft shoe shuffle around the names. If your library name was other than 'Calibre Library' you could just import it with that name (e.g. Smokva's Books), and remove the default Calibre Library.
BR