First, log into your Hosting Control Panel (DirectAdmin). From there, scroll to the Extra Features section and click the "Select PHP Version" link.
Once the link is clicked, you will see a message indicating that the Select PHP version plugin is loading.
Once the plugin loads, select the PHP options menu by clicking 'Options'
Now you will need to edit the 'upload_max_filesize' value by clicking on the triangle next to the current value.
Once you've chosen your new value, the system automatically saves the value.