Change the maximum upload file size

I have a website hosted on a PC I have no access to. I have an upload form allowing people to upload mp3 files up to 30MB big. My server side script is done in PHP. Every time I try and upload a file, I receive an error claiming that the file exceeds the maximum size allowed, so I need to increase the size. My research on the web suggested changing the `.htaccess` file which I do not have access to, so that won't work. Others suggested that I should add a custom `php.ini` file to my root which did not work. Any other suggestions?