Install OSX on Macbook Air which currently only runs Windows 7 I have a mac book air, which was formatted a long time ago, and only has windows running on it.

I would like to run Mac OS again instead of windows. Or if that isnt possible, have both OS's.

How can I get Mac OS installed on this machine again?
The easiest way is probably to use OS X internet recovery: 


Press cmd+alt+R at startup
Open the disk utility from the opening menu
Reformat the disk to HFS+ Journaled
Close disk utility and go to install OS X


This procedure will delete all your data and Windows completely.