Factory Reset

Hello. I recently bought a used computer for my sons. I need to do a factory reset in order for it to be back at "out of the box" settings. I would really appreciate any and all help.

The computer is an HP Pavilion PC and Monitor in one.
1.5 GHz AMD Athlon Dual-Core Processor
2GB (2x1GB) RAM
320GB SATA Hard Drive
SuperMulti DVD Burner with LightScribe
ATI Radeon HD 3200 Graphics
18.5" LCD Display
Integrated WebCam and Microphone
802.11b/g Wi-Fi
Windows 7 Home Premium (64-bit)

THANK YOU!!!!