I just bought a second-hand mini-pc and there is Zorin + W10 installed on it.
As it's for a remote control without screen purpose to control it from my W10 laptop I can't leave Zorin boot first on the mini-pc. I have try to change stuff in the BIOS but can't find a way to force the mini-pc to boot with W10 first without having to choose.
If you don't plan on using another OS it's probably best if you completely wipe the hard drive and install W10 only. This way you will have that much space available, and the issue with the bootloader will also be resolved.