Step1: Remove all the RHEL specific Packages
Run the following 3 commands to remove the packages.
sudo su —yum remove rhnlib abrt-plugin-bugzilla redhat-release-notes*
rpm -e --nodeps redhat-release* redhat-indexhtml
rm -rf /usr/share/doc/redhat-release*
Step2: Download Centos Packages
mkdir /TMP
cd /TMPrpm --import http://mirror.centos.org/centos/7/os/x86_64/RPM-GPG-KEY-CentOS-7yum localinstall -y http://mirror.centos.org/centos/7/os/x86_64/Packages/yum-plugin-fastestmirror-1.1.31-53.el7.noarch.rpmyum localinstall -y http://mirror.centos.org/centos/7/os/x86_64/Packages/centos-logos-70.0.6-3.el7.centos.noarch.rpmwget http://mirror.centos.org/centos/7/os/x86_64/Packages/centos-release-7-8.2003.0.el7.centos.x86_64.rpmrpm -ivh centos-release-7-8.2003.0.el7.centos.x86_64.rpm --replacefiles
Step3: Lets update the the server now with Centos Packages
yum clean all
yum update
update-initramfs -u -k version
update-grub
rebootStep4: Remove the old kernels once server is up (it would ideally take 1–2 min)
sudo package-cleanup -y --oldkernels --count=1
