[smallclone]

Simplest way, but not free Since you already have an uSD adapter (I presume) to write images to uSD card, then you'll need additional eMMC Module Reader Board for OS upgrade

First use CoreElec (full) Backup option of present uSD card installation, and save it to an easily accessed secure location. Then with Balena Etcher burn new, same version, CE image (using eMMC Module to uSD adapter) on a PC. Remove uSD card from N2 and attach eMMC to install CE. After it boots and all is OK with new installation, restore previously made backup. 
This way you'll get an exact eMMC system as is on uSD card.

Thanks for this. I don't mind paying more for a module reader. So do I have this right:

-Purchase the eMMC Module reader.
-Copy the existing CoreElec to a location on my PC
-Download Balena Etcher
-Insert eMMC Module Reader into the SD Card slot on my SD Card reader
-Burn the recently saved CoreELEC from PC to the recently purchased eMMC Module Reader
-Take the current SD card out of the N2+
-Then this is the bit I don't get...I insert the new eMMC module reader into the SD slot on the N2+  ? What happens then? I switch on and it just boots up? 

Or are you saying that what I need to do is burn an entirely brand new V19 version of CoreELEC onto the eMMC module reader? Then restore back up from the PC location?

I'm confused as to which stage my eMMC that is currently in my N2+ actually receives an updated version and how.

Sorry for being dumb.