1. install repository
rpm --import https://www.elrepo.org/RPM-GPG-KEY-elrepo.org
rpm -Uvh https://www.elrepo.org/elrepo-release-7.0-3.el7.elrepo.noarch.rpm
2. enable it and install kernel
yum --enablerepo=elrepo-kernel install kernel-ml
3. configure the grub
awk -F\' '$1=="menuentry " {print i++ " : " $2}' /etc/grub2.cfg
grub2-set-default 0
grub2-mkconfig -o /boot/grub2/grub.cfg
reboot
4. remove old kernels
package-cleanup --oldkernels