Repositories configuration:

On Fedora, standards repositories are enough, on Enterprise Linux (RHEL, CentOS) the Extra Packages for Enterprise Linux (EPEL) repository must be configured, and on RHEL the optional channel must be enabled.

Fedora 27

wget http://rpms.remirepo.net/fedora/remi-release-27.rpm dnf install remi-release-27.rpm
Fedora 26
wget http://rpms.remirepo.net/fedora/remi-release-26.rpm dnf install remi-release-26.rpm

RHEL version 7.4

wget https://dl.fedoraproject.org/pub/epel/epel-release-latest-7.noarch.rpm wget http://rpms.remirepo.net/enterprise/remi-release-7.rpm rpm -Uvh remi-release-7.rpm epel-release-latest-7.noarch.rpm subscription-manager repos --enable=rhel-7-server-optional-rpms

RHEL version 6.9

wget https://dl.fedoraproject.org/pub/epel/epel-release-latest-6.noarch.rpm wget http://rpms.remirepo.net/enterprise/remi-release-6.rpm rpm -Uvh remi-release-6.rpm epel-release-latest-6.noarch.rpm rhn-channel --add --channel=rhel-$(uname -i)-server-optional-6

CentOS version 7.4

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

CentOS version 6.9

wget https://dl.fedoraproject.org/pub/epel/epel-release-latest-6.noarch.rpm wget http://rpms.remirepo.net/enterprise/remi-release-6.rpm rpm -Uvh remi-release-6.rpm epel-release-latest-6.noarch.rpm

remi-php72 repository activation

Needed packages are in the remi-safe (enabled by default) and remi-php72 repositories, the latest is not enabled by default (administrator choice according to the desired PHP version).

RHEL or CentOS

yum install yum-utils yum-config-manager --enable remi-php72

Fedora

dnf install dnf-plugins-core dnf config-manager --set-enabled remi-php72

PHP upgrade

By choice, the packages have the same name than in the distribution, so a simple update is enough:

yum update

That's all :)

$ php -v PHP 7.2.0 (cli) (built: Nov 28 2017 10:27:47) ( NTS ) Copyright (c) 1997-2017 The PHP Group Zend Engine v3.2.0, Copyright (c) 1998-2017 Zend Technologies     with Zend OPcache v7.2.0, Copyright (c) 1999-2017, by Zend Technologies     with Xdebug v2.6.0alpha1, Copyright (c) 2002-2017, by Derick Rethans

Known issues

The upgrade can fail (by design) when some installed extensions are not yet compatible with  PHP 7.

See the compatibility tracking list: PECL extensions RPM status

If these extensions are not mandatory, you can remove them before the upgrade, else, you will have to be patient.

Warning: some extensions are still under development (xdebug...), but  it seems useful to provide them to allow upgrade to more people, and to  allow user to give feedback to the authors.

More information

If you prefer to install PHP 7.2 beside default PHP version, this can be achieved using the php72 prefixed packages, see the PHP 7.2 as Software Collection post.