how can i restore a previously owned mac book air?

Welcome to the Apple Support Communities

First, open  > About this Mac, and see Version. If it's 10.8, you have to purchase Mountain Lion to be able to reinstall OS X, so open App Store and purchase Mountain Lion.

Then, to restore the computer to default settings, follow these steps:

1. Press Command and R keys while your Mac is starting to start into OS X Recovery, and open Disk Utility.

2. Choose Macintosh HD on the sidebar, go to Erase tab and erase the disk.

3. Close Disk Utility and reinstall OS X.

If it's 10.7, call Apple to purchase OS X Lion > http://support.apple.com/kb/HE57

If it's 10.6 or 10.5, you should have the Mac OS X DVDs that came with the Mac, so you need an external optical drive or another computer with Remote Disc to reinstall OS X

Should be a Recovery volume on the disk for 10.7 if that's what's running on the machine. As Mende says, restart with the R key or the C key held down to get to that. If it's ot 10.7 or 10.8 installed, 10.8 is only $29 from Apple via download, assuming the computer is new enough (made in the last few years) to run that. It's not like Microsoft where a new OS copy is hundreds of dollars 🙂

What year was your Air made? Apple Logo, About this Mac.

If it did not originally come from the factory with Lion Preinstalled then you can not legally reinstall Lion and you would need the original owners Apple ID to do that.

That is why we need to know what year it was made. It may of come with an earlier version of OS X and the seller should of supplied the original system discs if it is older the a Mid to Late 2011 model.

dayre28 wrote:

do you have to have mountain lion to restore it? i just want it to factory settings. i have mac os x 10.7.5

With all due repsect, you CAN legally install Lion/10.7 - although if you don't have an original distribution to dedicate to the machine, then you would have to buy that somewhere. You won't need the original owner's AppleID or anything else.

Actually, wipe-and-reinstall would be the smart thing to do in case the previous owner had left any questionable files or malware.

He Can Not Reinstall Lion if the system did not originally come with it unless, Yes, he buys it.

Without knowing the age of the system No one, Not even you or me, can tell if the seller sold a Mac that Should Not of had Lion left on it.

Michael King wrote:

With all due repsect, you CAN legally install Lion/10.7 - although if you don't have an original distribution to dedicate to the machine, then you would have to buy that somewhere. You won't need the original owner's AppleID or anything else.

Actually, wipe-and-reinstall would be the smart thing to do in case the previous owner had left any questionable files or malware.