If you want to learn a bit more about Apache ACE, I can recommend reading the following two articles on the ACE website:
To be honest, if all you want is to updated a set of bundles on startup, then ACE is a bit overkill. It can be used to manage multiple "targets" (frameworks running OSGi) from a central server, automatically pushing updates to it and managing large sets of bundles and other artifacts, grouping them in features and distributions.