Apple

Well if you're dead fixed on doing it, I'd recommend looking at iFixIt teardown of similar model to get a feel of how to get to the component.

iFixIt seems to suggest the early 2014 Air is similar to 2013 Air :

The new Airs are pretty much the same computers as the 2013 models, with the same meh (4 out of 10) repairability.

So you'd probably follow:

• 11 Inch Repair Guide; or
• 13 Inch Repair Guide

See how to do "Logic Board Replacement", which will give you the required tools and procedures to safely remove the logic board (and perform in reverse to reinstall it).

Looking at the 2013 teardown, the memory module appears to be on the backside of the logic board, so you'd probably need to look at your logic board to see what chip yours is using -- it may be different than the 2013 teardown, so don't take that photo at face value -- then find appropriate upgrade from the same generation of your Early 2014 MacBook Air. Once you have the part, because of the size and location, you'll most likely need to use heat gun to remove the chip. After which, you'll need the correct template to reball the soldering points, and use the heat gun to solder the new chip into place.

I will say this again. I'm already not the typical nerd in my circle of nerds, and despite having seen plenty of videos and tutorials on this subject, I do not feel confident that I can do this procedure correctly. I don't feel this is something vast majority people will be able to do, even if they have access to the applicable tools. The upfront investment and chance of success is just not a worthwhile endeavour. It would be much more prudent use of money and time to buy a new refurb unit, which will run circles around the upgraded unit.