When you undo a check out, a read-only copy of the latest revision is left in the workfile location and the revision number that was created during check out is released. No changes are checked into the Dimensions repository.
To undo a check out:
In the Solution Explorer pane, select the files, projects, or solution for which you want to undo check-out. Right-click and select Undo Checkout.
About File and Version Management
Setting Up Source Control
Synchronizing with Dimensions CM Projects
Checking Out Files
Checking In Files
Accessing Specific Revisions