I have no Lenovo-specific info, but the major OEMs like Dell, Lenovo, Acer, etc should have similar policies.
Any "recovery" would take you back to factory specs as the PC was when it left the factory, with whatever applications and configuration Lenovo included.
You probably have several choices, such as:
1: Contacting Lenovo and requesting "recovery disks" for your PC. They may be free or there may be a charge. You'd then run these discs from your DVD drive.
2: Making your own recovery disks by using certain menus and applications already on your PC. You'd need to have a burner and some blank CDs or maybe DVDs.
3: Recovery using a probably hidden "recovery partition" placed on your hard drive by Lenovo at the factory.
All 3 of these would accomplish the same thing.
I don't know which of those choices you have, but it's a 99% certainty you can do at least one of them. Someone with Lenovo specific knowledge will have to help you. Most likely it's a fairly simple procedure involving knowing where to look---which menus, which of your applications, your Windows Control Panel, etc.
You would lose any personal data if you don't back it up separately.
You would lose any changes made to the system since you bought it. For instance, any programs you've installed since purchase. You'd have to reinstall them.
Your PC should have a sticker on it somewhere, placed there by Lenovo, that contains a 25 character "Product Key". If you can find this, you can always do a "clean install" of Windows, which some people prefer, but which would NOT include Office or anything additional.
Do you have the Office install discs? Did you just get a trial version or a full unrestricted version?
I should add: I would NOT assume that this procedure will solve whatever slowness issues you are having.