That's because of the default upload limit of PHP.
You need to create a file named .htaccess (note the period in front of the name). Put the following two lines into the file:
Code:
php_value upload_max_filesize 30Mphp_value post_max_size 30M
Upload the file into your forum directory (the same location where downloads.php is located.)
This will increase the size of the file you can upload to 30MB.
