Even though I had some experience with another board but, I still got confused, so many bits of information pointing different directions, mostly because I kept getting directed to 'Upgrade' forum posts. Use the Build Guide for details, but if you're getting overwhelmed take a break and see the notes below.

1. Copy files to Duet SD card. Get and unzip The D300vs Plus firmware : from GitHub here

2. Software on PC is needed to communicate with Duet board via USB. you will need to use this to send commands to it to get Duet to connected to your network and access web interface.

This is the instructions for above 'Getting Connected to the Duet Wifi' Only read the content 1 & 2 , ignore the stuff for 1.18 and after, this is where my head jus .t . . . % ( #@!

If your Duet already has RRF 1.19.2 installed you only need to copy the 4 folders from the latest 1.19.2 ZIP (gcode, macros, sys, www) onto the SD card installed on the Duet and restart/repower the controller. See the Duet Guide for instructions on getting the version and connecting via wifi