R5 to R6 Document Library upgrade and questions

This novice admin with little design knowledge is trying to reassign ownership of some documents and upgrade (if necessary) the design of a Document Library created with the StdR50WebDocLib template to the design template for Lotus 6X. Is upgrading the design going to cause any issues with the existing documents? Also, even though I am manager of the database, entries by other users (who have left our organization) with editor access cannot be edited, and therefore cannot be updated by any other users. Is there a way to reassign rights to existing documents created by others using Designer?