You can use the Undo Checkout command to cancel an existing checkout. This is particularly useful when you have modified and saved a file, and then later need to roll back your changes.
Depending on the options you set in the Undo Checkout Advanced Options dialog box, the Studio environment either leaves the working copy of the item on your local disk or replaces it with the latest source-controlled version. If someone has modified the item outside the context of the source control system, the retrieved version may not be the latest one.
To undo a checkout
In Solution Explorer, select the project.
On the File menu, point to Source Control, and then click Undo Checkout.
In the Undo Checkout dialog box, select the appropriate options, and then click the Undo Checkout button.