With an SSD, i5 and 4GB RAM, I'm pretty confident that there should be no performance issues with OS X El Capitan (10.11). However, I'm not sure if this is because they were possibly using MacBook Pro and consequently HDD (if no SSD upgrade done), since recent OS X versions are optimized for SSD, or if recent OS X versions are very RAM-hungry to run well. I read here and there that some users of MacBook from 2012 encountered performance issues when upgrading to High Sierra and upper. However,you have to stay to Mojave (10.14) or below if you still want keeping the ability to run 32-bit apps. Officially, the MacBook Air 6,2 can be upgraded up to Catalina (10.15). However, some users reported 4GB RAM being not enough for recent Mac OS X versions. It should run without problem a system like Windows 10.

The generous graphic card, the SSD and the relatively fast processor should still make it a very decent computer for office use. 500 GB SSD (replacement from 256 GB original one).I'm looking for feedback from those who actually upgraded their MacBook Air 6,2 (mid-2012) with i5 and 4GB RAM to any of these versions: El Capitan / Sierra / High Sierra / Mojave. I want to upgrade it to a newer version, without compromising performance, as I want the buyer being happy with his purchase. It is currently running OS X 10.7 Lion (for which Safari is obsolete). I have a mid-2012 MacBook Air 5,2 (13'' A14) that I plan to sell.

High sierra macbook air 2012