You can disconnect your channel from Google+ and switch back to a traditional YouTube username:
- Make sure you're signed into YouTube, and go to YouTube account settings
- Click the link that includes disconnect Google+, found below your email address.
- If you had an old YouTube username: You will then be asked to confirm that you want to revert your YouTube channel to your old username. Click OK and your identity will be reset to your old username. Your old avatar (if you had one) will be restored as well.
If you never had a YouTube-specific username: You will then be able to enter a YouTube username. Follow the instructions and then click OK. Your identity and Channel URL will be updated to reflect your new username, and your Google+ photo will no longer appear as your YouTube avatar.