change PHP version

Change Global (command line) php version (for laravel):

use this command :

sudo update-alternatives --config php

for more see link below :

https://bytexd.com/fix-laravel-return-type-of-illuminatesupportcollectionoffsetexistskey/

Change apache PHP version (for projects which you run with apache):

#(old php version)
sudo a2dismod php5 

#(new php version )
sudo a2enmod php7.1 

sudo systemctl restart apache2

https://superuser.com/questions/969861/phpinfo-and-php-v-shows-different-version-of-php