The WordPress revisions module can make backup copies of any page or post. A new revision is saved every time you save or update a page or post. The WordPress revisions history module, usually situated at the bottom of the Edit screen, will save up to 25 copies of your page or post. When you need to look back at previous copies, WordPress will allow you to compare the backup copy with a selected version of the page or post. If required, you will be able to update your current version with one of the previous saved copies.
If you cannot find the WordPress revisions module, you will need to turn it on in the Screen options tab at the top right of the Edit page.
To compare revisions, move the slider to the version you want to compare to.