I updated directly over a copy of MyHero II's High Sierra 10.13.6. First, I ran MulitBeast v10.4.0 to just update Clover. Then, I updated the network and USB kexts in /Library/Extensions folder. Rebooted, and I clone the HS disk including copying the EFI folder into the new disk's EFI partition. I downloaded the Mojave installer from the App Store and ran the installer.
I'll be using the Mojave installation only to test and get use to it. I will continue to use HS 10.13.6 until Mojave 10.14.3 comes out with all the major bugs worked out of the system.
Good luck! ..and have fun.