If you also amended the federal Form 1040 (1040X), you don't need to enter anything as there is a box to check that you are amending the federal too. And that's all Delaware requires for general amendments.
If you're only amending Delaware, you would type the reason you are amending and the associated line numbers. For example explanations such as "Additional income added and line XX increased" or "Corrected Form xx and line xx decreased" are fine. You can determine which lines changed by looking at your original tax return and comparing it to the amended form (prior to filing).