In One True Media how do u add sound clips?

[Doggie Luva]

What I mean Is how do I take off the sound that the video came with because there is talking in the bg.
After that how do I add 2 music clips where there is screaming, like those videos where something jumps out at u, thats wat I mean
So I dont want any noise except the screaming for a few seconds

if i cant do this on one true media where can I do it