First
Don't touch the kernel, please, if you need space there's other places you can chop and vandalize. There's a reason you always have two version of the kernel in the system. And apt always tells you to remove the old (3rd one) when you upgrade it.
Second
apt has space to fix itself, why didn't you answer Y (yes) when you ran sudo apt install -f?
Just run
sudo apt install -f
answer yes, and then run
sudo apt autoremove
Now if you want to make space...
Run the command as root
# du -h / -d 1 --exclude=/home
or with sudo
$ sudo du -h / -d 1 --exclude=/home
(choose one)
There we could see which directory uses more space, I bet and probably is /var. The moment you provide that feedback we can continue. Because the nature of you problem is space and I can't tell you to run commands that need space to work.
I could tell you, as an answer, to shrink /home to give more space to /, but that will need a lot of time and you could lose data in the process, so the best way now is to go step by step. You more than an answer need a solution and I can help you if you keep giving us the information.
One thing is sure, you have space to make. No way you need 19 Gigs in the root mount point
3
Run this command and paste the output please:
$ df -ih
And also as root run this
$ sudo su
# for i in /*; do echo $i; find $i |wc -l; done
# exit
4
Now (after you ran du on /) please run:
$ sudo du -h /lib/ -d 1
Also, we started to see what's your problem. Looks like you are out of inodes on /. I need to check what's on /lib and then we can start to do some stuff
5
Run every command and paste each output separately:
$ sudo du -h /lib/modules/* -d 1
$ ls -la /lib/modules/
$ uname -r
$ dpkg --list | grep linux-image
Run as root
$ sudo su
# for i in /usr/*; do echo $i; find $i |wc -l; done
# exit
(paste the output)