Restart your MBA, hold cmd+r till it is boot on recovery mode, erase your drive and do the rest.
Even though you don't have an installation disc, your MBA should automatically download the required files PROVIDED YOU HAVE A STABLE AND FAST INTERNET CONNECTION. The installation might take few hours. If you feel the progress has stuck for quite some time, you can check if it is unresponsive by checking the log.
I've tried this at least twice before and the installations were successful. The last attempt was 2 weeks ago when I tried to clean install Sierra.