How to restore my Acer laptop to factory settings?

I have an Aspire 5338 laptop, which i want to sell - i need to reset it to protect my data etc but i am not sure how to do this and i have a complication. The laptop originally came with Vista installed but i upgraded to windows 7 through direct download. Can i restore it with windows 7 or will i have to go back to Vista, something that will diminish my laptops value. Any advice would be appreciated.