To revert the templates, go to Style and Templates in the Acp of your forum-Edit templates-and then look for the Register templates and once you find them, under the right side where it says "Controls" click the Revert button. This will revert the template to its original state.
To upgrade your forum, make first a thorough backup of your database (make sure that it works), disable the mods and then overwrite your forum files with the set from the latest 4.0.2 package, minus the install.php file, and point your browser to the upgrader. i.e.
But in my opinion it would be best to first make a duplicate of your main forum at your test one and do a test run with the upgrade before you upgrade your live forum.
Hope it helps.
when i highlight Registration Templates the revert button is not clickable