Download the M4A to M4B converter software. A link for the software is available in the "Resources" section. Select "Save File" when a small window appears asking what you want to do with the file. The download now starts.
Launch the downloaded file and follow the prompts to complete the installation process.
Open the installed M4A to M4B converter program by double clicking the desktop icon of the program.
Click "Add Files" once the software opens and select the M4A files you want to convert.
Click the down arrow under the "Convert" button and select "To M4B." Click on "Convert" and the conversion process begins.