It is only for the current version that version number, change description and version state may be changed -- for earlier versions this information cannot be edited any more.
To change some aspect of a Document's version information,
to bring up the 'Modify' form.
to go to the section Change version info for Document name of that form.
Or
to display its Info page and
to bring up the 'Change version info for Document name' form.
to put the modifications into effect.