NOTE: you can only delete the questions you add. If the questions are passed from higher levels, then they can't be deleted.
From Memberships select Registration Fees & Forms.
Select Forms and then Forms made Available to me.
Click Use this Form at the start of the line you wish to select. This opens the form as editable.
Select the Questions & Layout tab.
To delete a question, click Remove on the line of the question. This selects the question for deletion.
NOTE: the question will delete once you click save.