To add files to existing beats, or replace existing files on your beats head over to
Dashboard -> Beats -> Upload
Click the 'Replace' option
Drop your files onto the uploader, or click inside the dashed box and select your files
Once your files have uploaded, you will be able to choose which beats you want to link the files to.
Select the relevant beat for each file and click Save
Click here to see how to upload tagged beats
Click here to see how to upload a new beat