Reverting a file will undo the changes you have made in the workspace and put the file back to its server revision. The file will be removed from the local changeset.
You can revert an individual file by selecting the 'Revert' menu or selecting the file and using the revert toolbar button. Alternatively you can select the 'Delete' menu on the local changeset. This will prompt whether you want to revert all the change items belonging to the changeset.