How to change the resolution of the Bash for a Debian VM?

What you basically want to do is change the resolution of the framebuffer. Here's the process I used (supposing that your desired resolution is 1024x768, and that Hyper-V's framebuffer supports this resolution):

1. Open up /etc/default/grub with superuser privileges: sudo nano /etc/default/grub
2. Uncomment/add the following lines:

   GRUB_GFXMODE=1024x768x32
   GRUB_GFXPAYLOAD_LINUX=keep

3. Save the file and exit: Ctrl-O, Enter, Ctrl-X
4. Run update-grub as superuser: sudo update-grub
5. Reboot, and (hopefully) enjoy a higher-resolution console!