updated NVIDIA drivers: black screen or login loop

Question

I've recently changed my Nvidia driver version & rebooted to

1. login loop
2. Black screen or TTY

This is not a exact duplicate of Graphics issues after/while installing Ubuntu 16.04/16.10 with NVIDIA graphics because

1. not installing nvidia drivers for the first time
2. I have not installed or upgraded to Ubuntu 16.04: this question isn't specific to 16.04

Some of the answers are the same but the question is not an exact duplicate.

The justification for this post is the "inaccessibility" of the "duplicate" post to new users like in these examples:

• 13.10 Saucy login issues; black screen, loop, and freeze
• Unable to solve login loop problem after installing Nvidia driver via run file
• Changing Nvidia Driver black screen
• Ubuntu 16.04 doesn't boot or gets stuck in login loop after install
• 14.04 login loop

There are a lot of questions like these one. Just search for yourself, so let's make one good specific answer for the new guys.