You need to add the ubuntu driver repo (sudo add-apt-repository ppa:graphics-drivers/ppa) to get newer drivers like 550, and 555. From my testing 545 is broken, and 535 is buggy. Just like windows, you should never install a driver package over an existing one; you need to purge them first. Here is how:
- Switch to nouveau
- reboot
- purge existing drivers (sudo apt purge nvidia*)
- run apt clean and apt autoremove to clean caches and unused headers
- reboot again
- install newer driver
The easiest way to switch to nouveau and install the newer driver is to use software-proerties-qt, the GUI from Kubuntu. It is in the apt repo.
If nouveau does not work for you, then I suggest that you have more problems than just the proprietary driver, as it should always work.
If the Software Properties GUI gives you grief, (like greyed out boxes which means your install is broken and its seeing modules it did not install even after the purge - likely because the module was running during a bad install) then you can manually install the driver meta package again with
sudo apt install nvidia-driver-xxx
If the kernel complains about a module, then make sure you are installing the one the kernel is complaining about, and then do the whole upgrade purge process again.
At this point, the gui should become unbroken.
I have found lately that installing a new Nvidia driver (not just update) may require a couple of reboots before the autoconfig figures things out. If it looks like it is logging into the desktop, but then sits with a black screen and cursor, then reboot and try logging in again. This happens almost every time with me, but a reboot or two solves it and the problem goes away until the next driver install.
These steps work for me even when the machine is completely bricked and I have to go into the recovery console or whatever its called.