@mayer
You can purchase a used 8GB logic board with a 1 year warranty for this machine here:
http://www.powerbookmedic.com/MacBook-Air-133-17GHz-Core-i7-Logic-Board---Mid-2013-p-26373.html
For $318.00, He could then sell the 4GB board on eBay for a $200 or more , How exactly is this a BS answer? It's took more effort than just saying NO you can't do this, furthermore Ebay is not the only place to source parts, in fact Ebay is ALWAYS a last resort for me. Not sure where the attitude is coming from. He ends up with the result he wants and becomes familiar with how to replace a logic board and on only costs around $100, Sounds like the correct answer to me...