One of the things that you can do with a Shift you do not want to work is to Post it to the Trade Board. This will enable any of your co-workers who can work your shift (without any conflicts) to claim it from the board and have it added to their shift schedules.
From the My Calendar tab, navigate to and then click on the shift you want to Post and select the "Trade Shift" option.
The next screen will be the Trade Shift screen and select the "Posting the shift to the Trade Board" option.
Click the Trade button to confirm your posting to the Trade Board.
Once you select the blue "Trade" button to finalize your posting, you should see the resulting change in your Shift Calendar. The Shift in question will no longer have the left-hand border color it did before, but now it will have a Grey border color, indicating that the shift is pending to be trading away. In this case, the Shift is on the Trade Board, waiting for a co-worker to claim it.
Once a co-worker does this, RosterApps will send you a confirmation e-mail that someone has picked up your shift, as well as send an e-mail to the person who picked the shift up. You will see that the shift in question has disappeared from your Calendar.
If you want to cancel a Shift you have Posted to the Trade Board, you can do so by clicking on that shift and selecting "Cancel Trade" in the pop-up menu.
However, you can only do this up until the point that someone claims the shift. After that, it is too late. You could speak with the person who claimed your Shift, but they are not obligated to return it.
If the Shift you Posted has not been claimed yet, you will see it represented on your Calendar as a normal shift, but with a Grey left-hand border. Click on the shift in question, and select the "Cancel Trade" option.