The two programs are closely related and you can test drive Wavepad prior to purchase.
In many (not all) cases, a right-click on the audio clip offers the option to EDIT IN WAVEPAD.
Click on it and WP opens. When editing is complete click the red X at the top-right and answer SAVE to the prompts.
The edited audio file will be placed on the timeline in Videopad.
UNlink A/V on the clip, if necessary, and drag the video to match the new audio. Then delete the old audio.