在CentOS7上将PHP从5.5.7更新到7.

I tried many times to update PHP from 5.5 to 7 on CentOS 7 but always unsuccessful. The installation seems always going well but when I checked php-v it is always:

PHP 5.5.7 (cli) (built: Jul  5 2017 12:03:23)
Copyright (c) 1997-2013 The PHP Group
Zend Engine v2.5.0, Copyright (c) 1998-2013 Zend Technologies
    with Zend Guard Loader v3.3, Copyright (c) 1998-2014, by Zend Technologies

Any idea how can I update?

Base repository of CentOS has no php7 packages.
You can use remi repo to install php7 on your CentOS 7.

Why Remi?

PHP package installed from remi repo will work as drop-in replacement for your current php5 binaries.
Remi repo is managed by one of PHP internals
Why not?

To install the Remi repository, we need to enable the EPEL repository first.

sudo yum install epel-release yum-utils
sudo yum install http://rpms.remirepo.net/enterprise/remi-release-7.rpm

Then Enable php 7.0 (You can use php 7.1+ too)

sudo yum-config-manager --enable remi-php70

Now it's time to install php7

yum install php php-common php-cli php-mysql

Great!!!
Now you have php7 on your system. You can confirm with :

php -v

Details Instruction on how to setup php on different OS : https://rpms.remirepo.net/wizard/