I would never say that unless I didn't know the answer! Do you still have the usb stick that came with the MBA that has Snow Leopard on it? If so, insert that into the usb port, restart the machine and hold down the "option" key. This will force the Mac to boot to a selection screen and from there choose the usb stick with Snow Leopard. Use that to erase the SSD from within Disk Utility Once that's done, reinstall Snow Leopard and once you have the app store on there, re-download the version of OS X that you want to run. Your previous purchases should be on there and should make it easy enough.
The only thing that you should be mindful of is making sure that all of the information that you need (pictures, movies, documents...etc) are backed up somewhere. Then once the MBA is up and running again, just transfer your info back over and that should be good. The whole process should take roughly 2 -3 hours depending on your internet connection speed.
If you no longer have that usb stick, then you'll either have to find one or purchase the usb superdrive, find a copy of OS X that's on a disc, and follow the same process as above.