Hi
Load your video clip to the media list and then drag it down to the sequence line.
The audio associated with the clip will be seen on the Audio track underneath.
Now Right click the audio track that you want to "Unlink". A menu will appear.
Select (left click) the option "Unlink sound clips". The audio will drop down to a lower soundtrack.
Left click and drag the audio a little to the right or left as this will "detach" it from the video and also select it. Now Right click it.
Select "Delete selected audio" from the menu. The audio will be deleted. (If you make a mistake you can restore it by Right clicking the video clip again and selecting "Restore sound clip"
** If you dont move it a bit, you may delete the video track as well. It seems to require "detaching".
You can now drag your replacement audio onto the soundtrack line.
Note: If you don't want to actually delete the audio, you have the option to mute it.
Right click the sound track and select "Adjust clip volume". Click the "Mute clip" box. Then OK.
The soundtrack will mute but will remain visible. You can now drag your replacement audio onto the lower soundtrack line.
Nat