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?