If you would like to update the audio file of one of your tracks, but not lose any stats or comments, or change the timestamp of the track, this is possible through the Replace file feature. This feature is currently available to Artist and Artist Pro subscribers.

Go to your tracks page (https://soundcloud.com/artists) and into the edit mode of the track whose audio you would like to replace, by clicking the three dots:

 

 

 

Then, tap 'Replace file':

Once you select your new audio file, the transcoding and uploading process will begin. Once the file has been 100% uploaded, click 'Save changes'.
 

 

If you upload a shorter file than what you have now, the comments will disappear from the shortened-track’s waveform, but still appear underneath on the track’s page in the comments section.