Restore Dell Inspiron Mini without CD

Hello, I wanted to restore my system. I am using Dell Inspiron Mini laptop. Can someone tell me how to do it without a CD? My mini laptop does not come with an optical drive so I wonder whether I could do a system restore without any disks. I went to Dell Service Center but they just didn’t help. My reason for this is because I wanted to sell my laptop so I want all my personal information to be deleted first. Can someone tell me? Thank you in advance.
