Q: How do I choose the $40.00 Icloud plan? When I attemp this, it doesn't allow me to click "next."

How do I choose the $40.00 Icloud plan? When I attemp this, it doesn't allow me to click "next."

The only way it allows me to click "next" is if I choose the $100.00 plan. The email that was sent to me says that I should upgrade or reduce storage because my plan will be reduce to 5GB as of September 30, 2013. Please advise.