When a level library is attached it is not possible to edit the Name, Number or Description of library levels.
If there is a need to rename these level values there can be no level library present. Detach the level library and then update the levels.
A library can also be attached via the configuration variable MS_DGNLIBLIST. If this library needs to be detatched in this case go to Workspace > Configuration and modify MS_DGNLIBLIST to no longer point to a DGNLIB path.
Levels and Level Libraries