Open an Internet browser.
Enter the URL for the conversion application into the address bar (see Resources).
Click inside the box labeled "File" to select the MPEG-4 file to edit.
Go to the MPEG-4 file and double-click to enter it into the input box.
Select the "MPEG-4 (.mp4)" option from the box labeled "Input Format."
Leave the "No Video Preset" option selected in the first "Output format" box.
Select the "MPEG-4 (.mp4)" option from the second "Output Format" box.
Scroll down to the "Advanced Settings" section of the page.
Select either the "+1" or the "+2" option in the "Sound Volume" section to increase the volume of the file.
Select a larger file size in the "Audio Quality" section, if needed.
Click the blue "OK" button to make the changes to the MPEG-4 file.
Test the volume of the edited MPEG-4 file by playing it in a compatible audio player.