You might want to ask in Synology forums, as it’s not really a Xibo related question, I personally do not know if synology is handling php.ini in a different way.
Although it seems rather similar - https://forum.synology.com/enu/viewtopic.php?t=114636
I assume there is some sort of control panel as well, so you probably can use that to restart web server.
If you’d need to adjust more values please have a look here How do I upload files bigger than 2MB / How can I increase the upload file size limit?