The older versions may be used in some situations when the system is started with other than the default startup settings. Which versions are used in that situation depends on the configuration of your boot loader.

If your system is configured to use grub as boot loader, the configuration file /boot/grub/grub.conf will show you which kernels are still configured as bootable.

On many systems, /boot is a separate partition and freeing up space there may not create extra space in the other file systems. Sometimes /boot is also mounted as readonly and deleting the files is not possible in that case, unless the partition is remounted with read-write permissions.

what does df -h give as output ?

I see. So deleting those files as will free space in a partition I can't normally touch anyway. That would be pointless!

Found a culprit with the disk analyser - very large Apache log and error files.

df -h was telling me 49Gb of 50Gb was used and I was getting the low space warning in the desktop. Deleting the Apache files has freed up over 20Gb! So I should be ok now. Thanks.

Good to hear you have found the cause of your full disk.

Don't forget to check the tmp path as many web plug-ins use it but fail to clean up on exiting.

Yes, your tmp and log files (especially error logs) fill up a lot of webdisk space! I'm glad you got that one sorted out. :)

Also, if you can access the package manager, either via UI or terminal, you can look up your list of installations and get rid of what you don't need anymore (especially outdated and no longer used libraries).