You can cancel a scheduled income by selecting the one you wish to cancel from your transactions list to open the edit screen and then clicking on the delete button. On Web, the delete button will appear as a grey button that says "Delete". On Android it will be a trashcan button in the upper-right, and on iOS it will be a trashcan button at the bottom of the screen.
You can find all of your scheduled transactions (including incomes) at the top of your transactions list. Also, deleting a future scheduled transaction will not affect instances of that transaction that have already posted.