If you check out a file from a library on a site, make changes, and then decide 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, and the file is made available again for other people to edit.
You can undo the check-out for a file if you were the person who checked out the file or if you have permission to change the library — for example, if you are a site owner. You should be careful if you are undoing the check-out for a file that is checked out to someone else, because any changes that the person made to the file after checking it out are overwritten.
If the library is not already open, click its name on the Quick Launch.
If the name of your library does not appear, click View All Site Content, and then click the name of your library.
Point to the file for which you want to undo the check-out, click the arrow that appears, and then click Discard Check Out.
When you are prompted to confirm that you want to discard your changes, click Yes if you are sure there are no changes that you want to save.
Note: If versions are being tracked for the library, any changes that you made to the file while it was checked out do not become part of the version history.