(original post: @triantares)
- Determine the kernel version you are running with
"uname -r"
- Find out what kernels are available:
apt-cache search linux-image"
and determine which one you want/need. Stick to the same type of kernel, only bump up the release number ... current is 5.5.0-0.bpo.2
- Install it: `"api linux-image-[version_you_chose] linux-headers-[same_version_chosen]"
- Wait until the install finishes. There will be a lot going on in your terminal screen, don't be alarmed.
- Reboot
If it won't boot the new kernel then boot into the old via "advanced options" in the grub start-up screen.
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all the options are now in the same main window, without the useless "rescue" ones but listing both kernels if you have 2 (or more) installed, also, it remembers your last selected boot option 
What do the "rescue" ones even do?
This also means that you will never get an opportunity to troubleshoot a system you've been shut out of.
Like an old machine that you forgot the user password of.
Rescue isn't useful there I agree but there
Always has to be a way to get a grub prompt !!!!!!!
This must be the most user-unfriendly idea you have ever had. 
Might as well delete this too then:
https://forum.elivelinux.org/t/lost-password-in-centos
This locking out is about as bad as any Windows solution.
iirc you can just press C for a grub prompt, and E to edit the option.
i think that the "rescue" option should be there.
Well I don't know about unencrypted filesystems but encrypted systems certainly do not give a prompt.
I have a small Howto on how to change a password on an existing system which --- can also be used to edit grub to reflect the wanted changes on a non-booting system but that would be a longer story.
resetting password using "chroot" on encrypted (lvm) filesystem.
Boot up live session ... in console mode will do for our purposes, which is a lot faster.
Become root with "sudo su"
, elive will not prompt for a password and decrypt the filesystem (in my case /dev/sda3 as it's a uefi boot)
"cryptsetup luksOpen /dev/sda3 lost-machine"
and enter the decryption password when prompted.
Mount the unencrypted filesystem on "lost-macine" (you'll want the / filesystem where passwords are stored):
"mount /dev/mapper/elive_vg-toot_lv /mnt"
- TIP: make use of hitting Tab (autocomplete) after /dev/mapper to show the system names available.
Check if it is indeed the wanted root filesystem with "ls /mnt"
and "mount"
to see if it is indeed mounted "rw" which is needed.
chroot into /mnt :
"chroot /mnt "
If you don't know the user name on the machine do:
"less /etc/group"
where you'll probably be wanting the adm: user ... or to show other users do
"less /etc/group |grep 100"
-
To change the root password simply type "passwd"
and enter a password for root and wait for the "successfully changed"
message.
-
If you need to change a forgotten user password, like in my case for "triantares" you give the same command with the wanted username added: "passwd triantares"
and after entering the new passwords and wait for the success message
And reboot the machine with Ctrl,Altand Del combo.
You'll find the passwords changed as wanted. 
Added this as a separate Howto.
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