Slices is a little out in the cold as far as our dm Server development process goes, so apologies for times when it drifts out of whack.
In general, we control the version dependencies of the "components" (we call them repos, meaning git repos, but that's not a great term) of dm Server such as the kernel using the component's build.versions file.
We use the same approach to control the dependencies of slices on other components.
To upgrade a single dependency of a component, we use the update dependency Ruby script in the dm-server/scripts directory, e.g.
This updates the relevant version in build.versions, certain properties files, Eclipse classpath files, Ivy files, etc.
~/dm-server/scripts/update-dependency.rb -v com.springsource.kernel -n <new version>