Switch to Console in Ubuntu 18.04 - How to Leave GUI?

To install the graphics driver I need to exit GUI / Gnome and go to the terminal. How can I do this in Ubuntu 18.04? Ctrl(STRG)+Alt+F1...F7 does not work, neither on the desktop, nor on the login screen...

In Ubuntu 18.04, they have changed things around and you cannot get to tty1, it is always showing the display manager / login screen. If you log in, you then cannot get to tty2 because it becomes the GUI for the first logged in user. The tradition of both GUIs showing on tty7 has ended.

You can get to tty3 by pressing Ctrl+Alt+F3, tty4 by pressing Ctrl+Alt+F4, tty5 by pressing Ctrl+Alt+F5 and tty6 by pressing Ctrl+Alt+F6.

You can then switch between tty3-6 by pressing Alt with the appropriate F-key.

Finally, you can get back to the GUI with Alt+F1 for the login chooser or Alt+F2 for the logged-in user's desktop.

I'm on an 18.04 laptop.

I have to press Fn as well as Ctrl+Alt+F3.

Assuming you're on a Desktop or Laptop, just use:

Ctl+Alt+F2

Or, you can boot into single-user mode, although you probably don't want this as getting internet in this mode can be tricky.

My preferred way of entering recovery mode is to set

init=/bin/bash

via grub. Then, run:

mount -o remount,rw /

after you get a shell. Then, you can try using

ifconfig eth0 up

for ethernet. If you use WiFi, try this question.