How to factory reset a Lenovo desktop?

My home desktop is running terribly slow I was wondering if anyone could tell me how to factory reset it without a windows installation disc, F11 doesn't prompt anything when s press it during start up and I can't seem to find a simple factory reset option anywhere, restoring it to an earlier time isn't any help seeing as I'm trying to wipe it clean and start from scratch, if anyone has a solution id appreciate the help, thank you.