You have to upgrade to 19.7, patch 19.7 and then upgrade to 20.1 etc....
Alternatively, if you are willing to save the configuration and either restore/recreate it, you can write a copy of the latest system install to usb, boot the box from the usb stick and install from the live system.
Might be significantly faster that way :)
Alternatively, if you are willing to save the configuration and either restore/recreate it, you can write a copy of the latest system install to usb, boot the box from the usb stick and install from the live system.
Might be significantly faster that way :)