Deleting or removing the linux kernel

For the custom compiled kernel one has to remove the following files/dirs:

1. /boot/vmlinuz*KERNEL-VERSION*
2. /boot/initramfs*KERNEL-VERSION*   (or something similar)
3. /boot/System-map*KERNEL-VERSION*
4. /boot/config/*KERNEL-VERSION*
5. /lib/modules/*KERNEL-VERSION*/ 

Then update the grub configuration file

$ grub2-mkconfig -o /boot/grub2/grub.cfg

 Restart the system

$ reboot

 Test which kernels are installed (for Fedora):

$ rpm -qa kernel

 Test which kernel is running:

$ uname -mrs
$ uname -r