You can specify an upload schedule for a scheduled post in the post dialog. In this dialog, you can either use a pre-defined schedule or use something custom.
In the post dialog, go to 'Date & Time:
Click on 'Never' in the repeat select box.
Select either one of the pre-defined options, or click on 'Custom', if those do not fit your schedule
If you've clicked on custom, you can now specify the number of days between posts yourself.