I offer two shipping options Flat rate courier and store pickup.

and I offer two payment options PayPal and Cash on pickup.

If a customer selects the flate rate courier option on the 'Delivery Information' page when they progress to 'Payment Information' page they still get the option of 'pay cash on delivery'/pickup.

How do I change it so that if they select a courier dispatch the 'pay cash on delivery'/pickup option does not show?

I am using the ZJ Black template

Many thanks in advance. Once I have this resolved I can go live.