Neowin discusses the Windows 8 reset and refresh process, you can learn about it over here.
For those who do not need to completely clean the machine, another option exists. The "Refresh" option allows you to take your machines back to a fresh install but all of your settings and files will remain in place. Refreshing your machine follows the process below:
The PC boots into Windows RE.
Windows RE scans the hard drive for your data, settings, and apps, and puts them aside (on the same drive).
Windows RE installs a fresh copy of Windows.
Windows RE restores the data, settings, and apps it has set aside into the newly installed copy of Windows.
The PC restarts into the newly installed copy of Windows.