To remove a discount, first go to the Operations tab on the left hand side. 

Next, apply the filters you need to see the unit you'd like to remove the discount from.

Select the checkbox next to the unit whose discount you'd like to remove.

Click the menu button as shown below.

Click on "Assign/Remove Discount".

On the pop-up menu that appears, click "Assign Discount" and change it to "Remove Discount"

Select the discount you'd like to remove, and if you'd like to remove it from an existing lease if a tenant is currently in that unit. Click "Remove Plan".

You've successfully removed a unit discount!