Answer:
From the GRUB command line, type exit. This should take you to the computer's bootloader. From there, select to boot from the Windows partition (probably marked C:).
If the method described in the first paragraph doesn't work, restart your computer and press F12 many times while the computer boots up. This should take you to the computer's BIOS, where you then need to navigate to the bootloader from and select to boot from the Windows partition (probably marked C:).