How to upgrade my MacBook Air from 10.6 to 10.9? I was given a MacBook Air from my step mother because she never used it. I tried upgrading everything but every time I try to update it, it stays the same old version. Do i need to go to the store first? 

It's still on OS X 10.6.8
Open the Mac App Store (/Applications/App Store.app)
Download the OS X Mavericks app.
Run it from the /Applications folder if it doesn't automatically run.
Follow the instructions.