You can switch a workspace to another stream by right-clicking the workspace and selecting 'Advanced | Switch Workspace'.
If the workspace contains changes then these changes are first shelved as described in Chapter 12, Shelving. The workspace is then switched to the new stream and the changes are unshelved as described in the section called “Unshelving Changes”. If the same files are different in the new stream then the Resolve Tool will launch allowing you to merge your changes with the new stream files.