How to access the server/root folder?

Hi,

I’m trying to increase the maximum upload size of a WordPress website, and looks like I need to create a php.ini file on the server, but I don’t know if I can have access to the server/root folder. Another company built the website, and I have only been editing the contents and making small template changes on WordPress- do I have access to the root folder or only the people who built it have it?

Thank you so much!