Open Terminal
Type: sudo vi /etc/default/grub
Find the line starting with GRUB_CMDLINE_LINUX_DEFAULT, and add video=hyperv_fb:[the resolution you want]. The resolution I want is 1280×720. So my line ends up looking like this: GRUB_CMDLINE_LINUX_DEFAULT=”quiet splash video=hyperv_fb:1280×720″
Write the changes and quit vi.
Run: sudo update-grub
Reboot the virtual machine