It depends if you want to restore previous IIS configuration or if you want to reset completely IIS and loose all data/config:

There are automatic backup under %systemdrive%\inetpub\history but it may not help much if you already made lots of changes.

http://blogs.iis.net/bills/archive/2008/03/24/how-to-backup-restore-iis7-configuration.aspx

You will have to regularly back up manually using appcmd.

If you try to reinstall IIS, please first uninstall IIS and WAS via Add/Remove Programs, and then delete all existing files under C:\inetpub and C:\Windows\system32\inetsrv directories. Then you can install again cleanly. But the key thing here is to make sure you uninstall the Windows Process Activation Service or otherwise your ApplicationHost.config will be still around. When you uninstall WAS then your configuration will be cleaned up and you will truly start with a fresh new IIS (and all data/configuration will be lost)