This is a common issue that I haven't seen many answers for on the internet. When you are using Linux as your host machine and you are connecting to another Linux machine over VNC you CANNOT use Ctrl+Alt+F1 to change virtual consoles as it sends the keys to your actual local machine.
In many versions of Linux you can cycle through virtual terminals including over VNC using this:
Alt + Left Arrow or
Alt + Right Arrow
This does not seem to work if you are running Xorg already though (at least in Linux Mint).