If you want to use a PHP script to upload the files, you have to change the PHP *_max_* values.
Depending from your server configuration, e.g. if runing PHP as CGI, you can put a php.ini file where your upload script is, with the following settings.
upload_max_filesize = 40M
post_max_size = 50M
To check if it i working create a php file and put this in it
But changing the *_max_* values might create problems with PHP memory, either-way you must play with the settings and see if it works for you.