change in the older version of the document type

Hi gurus,

I have created two versions 00 and 01 for the document type, is it possible to do a change of version 00 if the user has the authority. Both the versions are in the same status as in work (is it possible)

when will we create a version for a document ( if there is any change in the document or when u upload a new document)

kindly explain me clearly gurus.