Best answer by djraveinpeace
Thanks for visiting the help forums :)
This is possible if you have a pro or pro unlimited soundcloud account. If so you go into the edit mode and there is an option to replace the file. Its then simply a case of uploading the new file and saving the changes. You will not lose any of the stats or comments that the track has already gained.
The below link will explain & illustrate the process in full:
If you have the regular free soundcloud account then, unfortunately, this option isn't available and you would only really have the option of deleting the original sound & then uploading the revised version. This also means that any likes, shares, play stats etc would all start from scratch on the new upload.
I hope this helps :)