Create a web page that runs "phpinfo()". One such as:
<?php echo phpinfo();?>
would do. Just call it something like "info.php" and then call it up in your web browser. The results will be quite lengthy, but the item that you are looking for is called "upload_max_filesize".
Once you have done this, please remove or move the file out of your website directory. The phpinfo gives out a great deal of information about your website and should not just be left "lying around" to be accessed by a web page unless you need it.