Omeka-S upgrade error from 1.4.0 to 2.0.0

How can I fix this error :

Parse error: syntax error, unexpected ‘?’, expecting variable (T_VARIABLE) in /vendor/doctrine/dbal/lib/Doctrine/DBAL/DriverManager.php on line 137

Omeka S 2.0.0 (and the current latest version, 2.0.2) requires PHP 7.1 or higher.

You’re getting this error because the PHP installed on your server is older than that.

Thank you for this information
I will try to active the correct PHP Version

Serge Normand