Upgrade an old CentOS server without internet

If you ever need to upgrade an old CentOS server to another "less" old version

Mount an iso of the CentOS version you want to upgrade to

# mkdir /media/CentOS
# mount /home/sysop/CentOS-6.10-x86_64-bin-DVD1.iso /media/CentOS/ -t iso9660 -o loop

Show current CentOS version

# more /etc/redhat-release

CentOS release 6.6 (Final)

Perform upgrade

# yum clean all
# yum --disablerepo=* --enablerepo=c6-media update

Transaction Summary
Install      24 Package(s)
Upgrade     392 Package(s)

Total download size: 412 M
Is this ok [y/N]: y

Downloading Packages:
Total                                                                                                                       129 MB/s | 412 MB     00:03
warning: rpmts_HdrFromFdno: Header V3 RSA/SHA1 Signature, key ID c105b9de: NOKEY
Retrieving key from file:///etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-6
Importing GPG key 0xC105B9DE:
Userid : CentOS-6 Key (CentOS 6 Official Signing Key) <centos-6-key@centos.org>
Package: centos-release-6-6.el6.centos.12.2.x86_64 (@anaconda-CentOS-201410241409.x86_64/6.6)
From   : /etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-6
Is this ok [y/N]: y

Reboot system

# reboot

CentOS release 6.10 (Final)
Kernel 2.6.32-754.el6.x86_64 on an x86_64

localhost login: