With your project on the timeline, audio clips can be deleted from the audio track. If a clip is linked to video, first right-click on it and UNlink.
If you want to mix the existing audio with a voice track, add narration and place that new track below the existing. Then lower the audio volume of the other track. Click the track's FX icon, then the green + sign, then AMPLIFY. Move the slider to the left. Points at which audio gain goes up or down can be plotted. Animation editor HELP.
After completing the changes, upload to YouTube either directly from VP or by making a VIDEO file compatible with YT standards and using their uploader.
The HELP file for YT seems to be working. Here's how it reads...
You can open the YouTube export dialog via one of the following methods:
From the Home Toolbar. Click the Export Video drop down button. Select the YouTube... option.
From the Export Toolbar. Select the YouTube button.
From the Export tab on the Main Menu. Select the YouTube... option.
Once reaching the YouTube export dialog, you can choose assorted settings that will be applied to the exported project.
After making your selections click on Create, to being the export and upload process.
If required the YouTube Authorization dialog will appear. Login to your YouTube Account, and follow the prompts to allow the application to access your online profile.