If all your projects use the same version of a shared folder then there will be no need to update the shared folder link. The shared folder will only ever have one version, and all versions will use this shared folder version.
Sometimes there is the need to support multiple versions of a shared folder within different versions. A classic example of this is using third party code. Suppose you are using the third party library 'Widgets' and Version 1 of your product uses the initial Widgets 1.0. You start developing Version 2 of your product using Widgets 1.0. Then you see that Widgets 2.0 has been released with some great features for Version 2 of you product, but you don't want to risk breaking Version 1 (which is now live and doesn't need these new features anyway). To do this you create a new version of the shared folder as described in the section called “Versions”. You update the version to contain the new Widgets 2.0 files. Finally you update Version 2 of your product to use Widgets 2.0 rather than 1.0.
To update a shared folder right-click the version and select 'Administration | Manage Shared Folders'.
Select the shared folder you want to update and press the 'Update Shared Folder' button. This will launch a dialog where you can select the shared folder version you want to update to.
This will submit a changeset in the version with the file adds, edit and deletes to update the shared folder.