When uploading an episode, click on "Publish at a later time?" to select a date and time for your episode to publish.
If you need to change the date/time of your scheduled post, you can do this from your dashboard. If you navigate to your dashboard, you will be presented with your scheduled episodes.
Click on the title of your scheduled episode, and then navigate to the edit page for the episode in question. Then click on the "re-schedule" button to select a new date.