Both scheduled and active review cycles can be deleted.
To delete a review cycle navigate to
'Admin' > 'Review Cycles '. Here you will see all the reviews you have created so far.
From here select which reviews you'd like to delete and select it. At the bottom of the page you will see a red button entitled 'Delete Cycle' as highlighted.
A confirmation pop up window will then appear.
If you're sure you'd like to delete the cycle click 'Confirm', if not click 'Cancel'.
Your cycle is then deleted and will no longer show up under 'Review Cycles.'