Intro
My small server has a dual-boot setup: I installed Windows first, then Linux Mint. GRUB handles the boot process and boots into Linux Mint by default.
If your setup is the same, you can switch between the two systems remotely using the method below.
Rebooting into Linux Mint from Any OS
Since GRUB boots into Linux Mint by default, you can just reboot.
Booting into Windows from Linux Mint
My Windows entry is number 2 in GRUB's boot menu (counting from the top, starting at 0).
So to reboot into Windows, there's a one-time setting that boots to the selected GRUB entry on the next restart and reverts to the default on the one after that.
sudo grub-reboot 2
sudo reboot
Rebooting from Windows into Windows
In this case, you need to reboot into Linux Mint first, then use the method above to reboot into Windows. It's a bit more trouble, but since I don't need to do it very often, I think it's a cost-effective solution.