You check documents into the repository to share them with others. You must have at least the Write permission on a document (or on one of its packages) to be able to check it in.
Note:
If you change the target (DBMS, OO language, etc) outside of the target family (such as moving from AS IQ 12.6 to 12.7), you will no longer be able to update the existing repository document and will need to save the model in a new location in the repository.