How do I change my workspace in Team Foundation Server 2005 and 2008?

I'm going to assume you mean "workspace", not "workstation", as your question doesn't quite make sense to me otherwise.

In Visual Studio, go to the Source Control Explorer (View->Other Windows->Source Control Explorer). At the top of the source control explorer window you should have a toolbar with a few buttons. Somewhere on that toolbar (for me it's at the right) there should be a Workspace dropdown. Just select the workspace you want to use from that dropdown.

First, you should active you workspace window.

1. choose the window menu
2. click Source Control Explore.
3. click Active button.
4. The Workspace window appears
5. click the WorkSpace name in Workspace window.
6. from the popup list choose the Workspace name you want.

Are you wanting to change the location of the files on the workstation? If so, here's how I do it:

1. Open Visual Studio
2. Open the Source Control Explorer window.
3. From the Workspace dropdown select "Workspaces..."
4. The Manage Workspaces dialog should show up.
5. Select the workspace you want to modify, and click Edit...
6. You should be able to adjust the folders from here.