Undo check-out and discard changes in a SharePoint library
If you check out a file from a library on a Microsoft Windows SharePoint Services site and then decide that you don't want to keep the changes that you made, you can undo the check-out. The changes that you made to the file since you checked it out are discarded. When you undo the check-out, the file becomes available for other people to edit.
Find links to more information about checking out files in the See Also section.
Click the Microsoft Office Button , click Server, and then click Discard Check Out.
When you are asked whether you want to discard the check-out, click Yes.