Changes to PHP must be written to a local php.ini file placed on your website.
If you for example wants to change the maximum size for uploaded files, you will have to create a php.ini file with the following content. You can place the file where ever needed - usually in the website root (/web/) on the FTP-server.
upload_max_filesize = 256M
In this case the maximum file upload size is changed to 256 MB.
NB. Changes to php.ini has a TTL (time to live/cache) on five minutes. This means that changes will take effect within five minutes.