@ Munky261-

1) you need to find the folder that has the sound file that you want to replace in it. To do this use the little green arrows on the top tool bar to move around the file system. You can also double tap on a folder to show contents. Double tapping on a file will open that file.
2) Make sure you have the 2 panes opened. If you only see one pane (ie: one file listing) then tap on the icon on the left of the top toolbar (looks kinda like a book with red,green & blue lines).
3)Navigate to the folder where the new sound file is stored using the methods in #1
4)Drag and drop from one pane to the other.

In general to delete a file: highlight the file and click on the trash can

There's also a help file - to access it tap on the ->| icon in the lower right corner.