Mistakes happen! If you've accidentally published the wrong MP3, there are some things you can do.
Creating a new episode
If your episode has already been downloaded, there is no way to have podcast apps delete the audio file that they currently have. In this case, the best course of action is to delete the existing episode and create a new one. This will ensure that all of your subscribers download a copy of the audio that you intend for them to hear.
Uploading new audio
If your audio has not been downloaded yet, you can visit the Edit tab of the episode dashboard and upload new audio. Click the X next to the existing audio and upload a new audio file. Click Save when your audio has been uploaded.