If you have Data currently in FMDesktop and want to keep that data connected from the 'old' space number to the 'new' space number - then the one by one method is the best.
If you can 'start' over, open the drawing in AutoCAD, do a group edit, delete all the records (you will lose all data on the space, equipment, occupant, etc...) then renumber the spaces and use the Convert to Spaces command to relink the spaces to the DB. Then Update your plans (Plan Views).