I apologize for not posting this earlier. If by chance you downloaded the Photo Channel Update, and you don’t like the new AAC, and you want to switch back to MP3—I am now here to help:

• From the main menu, click the “Wii” button
• Select Data Management
• Select Channels
• Select Photo Channel 1.1 and confirm you want to delete it
• Photo Channel 1.0, the original, automatically returns to the main menu

Link