[Mashiro]

The correct corresponding php.ini configuration file for Apache 2 should be /etc/php/7.1/apache2/php.ini in this case. If you use nano you can use CTRL + W to start a search and find the parameters to increase size, edit them and save the file.

As far as I remember everything starting with ; or : is a comment. So if the parameter for the size is commented make sure to remove the comment sign or the otherwise the change to it won't be applied as comments are ignored. Alternatively you can add the parameter yourself anywhere in the file (at the end probably the best option to be sure).