Help:Undoing an edit
If there has been an incorrect edit, or vandalism to an article, it may be necessary to undo the changes made.
In some cases (for example, if a vandal added or removed text, and unrelated constructive edits have been made since), the easiest way to undo past edits may simply be to edit the current page, deleting wrongly added text or restoring wrongly deleted text (this can be copied and pasted from a past version of the page).
Undoing a page to a previous version
However it may be more convenient to restore a particular old version of the page from prior to the changes you wish to revert. To do this:
Click the "view history" tab at the top of the page to display the page history.
Click the time and date of the earlier version to which you wish to revert. You will see a phrase similar to: "This is an old revision of this page, as edited by ***.***.***.*** (Talk) at 15:47, January 24, 2012. It may differ significantly from the current revision."
Important: in the case of vandalism, take the time to make sure that you are reverting to the last version without the vandalism; there may be multiple consecutive vandal edits or they may be interspersed between constructive edits.
Click the "edit" tab as you normally would to edit a page. (Above the edit box, you will see a warning similar to: "You are editing an old revision of this page. If you save it, any changes made since then will be removed.")
Complete the edit summary field (the abbreviation "rv" can be used to stand for "revert"; the edit summary "rvv" means "reverting vandalism").
Save the page.
If constructive edits had been made after those that you wished to revert, return to the page history to find those edits, and redo them by hand if reasonably possible.
You may also want to know about Rollback as a technique for undoing edits