Computer doesn't always resume from suspend

[ajgreeny]

What kernels do you now have installed?
Show the output of

ls /boot | grep vmlinuz

which will show us installed kernels. If you have only those two I would keep the old one but if you have more you can run

sudo apt autoremove

which should get rid of all except the two most recent versions.

[ash22]

This is the output

vmlinuz
vmlinuz-4.8.10-040810-generic
vmlinuz-5.4.0-54-lowlatency
vmlinuz-5.4.0-56-generic
vmlinuz-5.4.0-56-lowlatency
vmlinuz.old

[ajgreeny]

You may find running command

sudo apt autoremove

uninstalls that kernel for you but if not you could use synaptic.
You may not have synaptic installed as it is not a default application in most of the Ubuntu family any more but if you like a GUI it is so much more useful than Ubuntu-software or whatever it is now called.
You can use synaptic to search for specific packages that don't show in Ubuntu-software, and if you search for name only using 4.8.10-0 as the search term it should show you that kernel and any associated packages such as the linux-header packages that you can remove.