Updating a 'live' environment

What is the best practise for updating a 'live' environment?

More specifically: suppose I have a database that is accessed by several instances of an application (say, a load-balanced Seaside app), but need to change the objects comprising the database in any of the following ways:

(1) Add/remove instance variables to/from a class that is persisted in a MagmaCollection; (2) Add/remove indexes to/from a particular MagmaCollection (perhaps after the changes in (1)); (3) Re-factor some of the classes, thus making minor changes to the schema

... how could the database be updated? Is there also some way to update all the existing objects in the database to reflect the new changes?

Amir