How do I restore my Asus see netbook to factory settings without a cd?

I have a hp mini and I don't have any cd drive or the back up disk or and kind of disk. My laptop keeps saying that I have no disk space and I try deleting things but it won't let me. What can I do to delete everything but only leave the programs the laptop originally came with?

Currently I have everything backed up that I need to that is on my Toshiba laptop. I want to delete all the programs that I have installed on the laptop since I bought it, due to lack of memory left. But I am not sure of which programs I really need. So I thought I would restore it to the factory...

[ as a beginner pressed wrong tabs and miniturised all my programs now cannot read instructions as shown how do I undo this grave error

I have just brought an Acer laptop second hand, I turned it on and it came up with login details for some one else but I don't know the password. How do I restore the factory settings with out the disc?