Remove Old Kernels on Fedora, CentOS

Check Installed Kernels:
rpm -q kernel

Delete / Remove Old Kernels:
## Install yum utils ##
yum install yum-utils

## Package-cleanup set count as how many old kernels you want left ##
package-cleanup --oldkernels --count=2

Make Amount of Installed Kernels Permanent
Edit /etc/yum.conf and set installonly_limit:
installonly_limit=2