Can I put a retina display on my iMac?

There are two versions of the 2013 systems

• 2012/Early 2013 (iMac13,1)
• Late 2013 (iMac14,1)

So as you can see there is no difference with the internal display, the Early 2013 and Early/Mid 2014 all offer a Native display Resolution of 1920x1080 within the internal display.

Now the Late 2015 (iMac18,2) does offer a Retina 4K display with a native resolution of 4096x2304, with a "wide color" DCI-P3 gamut, and brightness of 500 nits. By default, it runs "pixel doubled" at 2048x1152, but also can run at scaled resolutions of 2304x1296 and 1560x1440.

The 2012 through to the non-4K Late 2015 use a different internal interface than the 4K Retina systems. While they look the same the 4K connector is physically bigger (more pins) And you can’t plug in the smaller internal non-retina cable into it.

So sadly you would need to replace both the logic board and the display which is just not economical.