You can remove them if are not planning to go back using them.
Those 3 easy steps will help you to clean up boot sector in SSH:
(login as root first)
1. Check what kernel you're using, and do not attempt to remove it:
2. Get list of all installed kernels
rpm -qa | grep -i kernel | sort
3. Remove old! only kernels
yum remove [KERNEL_NAME_AS_LISTED-EXCLUDING THE ACTIVE ONE]