Make sure you are using a USB stick v2 (black internal connector), not v3 (blue internal connector).
After downloading, unzip the files including folders to the USB Stick (Do not put the ZIP file on the USB Stick).
Insert the USB stick into the USB in the RUNNING vehicle. It can take up to 5 mins for the top of the screen to say it's updating.
Depending on so many factors, the update can 30+ minutes (personally it's never taken more than 15 mins for me).
It will then advise you that you can remove the USB stick. Then turn off the vehicle, open the drivers door to shut down
all electronics. Wait a few minutes, then restart the vehicle, and check that you have to new version installed.
I hope that helps..