This guide is for CentOS Linux systems running PHP 5.3 and up.

Start by logging into WHM and making sure the server is on Apache 4. Use EasyApache 4 to upgrade if necessary.

To upgrade PHP 7, SSH into the server and download Remi and EPEL Repository:

$ wget -q http://rpms.remirepo.net/enterprise/remi-release-7.rpm
$ wget -q https://dl.fedoraproject.org/pub/epel/epel-release-latest-7.noarch.rpm

Enable the respositories:

# rpm -Uvh remi-release-7.rpm epel-release-latest-7.noarch.rpm
FOR PHP 7.0 EXECUTE:
# yum-config-manager --enable remi-php70
FOR PHP 7.1 EXECUTE:
# yum-config-manager --enable remi-php71

Then upgrade to PHP 7:
# yum update