Here is a step by step process on how to reformat your hard drive, with the OS intact and fresh.
I. Windows Home button
II. Control Panel
III. System and Security
IV. Look under Action center, should be a "Restore your computer to an earlier time" Option under Action Center; Click on it.
V. Recovery, Then click on "Advanced Recovery Methods", the bottom option should be "Restore your computer to factory settings"; Click on that, and then follow the step's that it gives you afterwards.