1. Be sure you are notrunning the kernel you plan on removing:
Type uname -r in terminal and it will display the kernel using by your system.
Or You can use the uname -a in terminal to check what kernel is currently used by your server:
2. Then, decide which kernel you want to delete:
Open the terminal and type sudo dnf list installed kernel or you can use rpm -q kernel. It will list all the kernels on the system.
3. Remove old kernels manually
Type this command sudo yum remove <KERNEL NAME> in terminal and then type the kernel version do you want to delete.
4. you can delete the old unused kernel automatically by using this command.
package-cleanup --oldkernels –count=1
5. You can check that old kernel is deleted or not by using this command.
rpm -q kernel
It will display the list of kernel on your system after deleting the old one.