changing laravel project from php5 to php7

I have an open source laravel project using php 5, when i tried to add the debugbar i get the message below. Your requirements could not be resolved to an installable set of packages. Problem 1
- doctrine/inflector v1.2.0 requires php ^7.0 -> your PHP version (5.6.31) does not satisfy that requirement.
- doctrine/inflector v1.2.0 requires php ^7.0 -> your PHP version (5.6.31) does not satisfy that requirement.
- doctrine/inflector v1.2.0 requires php ^7.0 -> your PHP version (5.6.31) does not satisfy that requirement. - Installation request for doctrine/inflector (locked at v1.2.0) -> satisfiable by doctrine/inflector[v1.2.0].

I need solution to this problem and a way to change the php used to php 7 please!!

via Chebli Mohamed