Q: Downgrading iCloud problem on macbook

Hi, I'm having a problem downgrading my iCloud account from 20gb to the free 5gb via my macbook.  I performed these steps: Apple > System Preferences > iCloud > Manage Storage > Change Storage Plan > Downgrade Options.

My current plan is shown as 20gb.  When I try to click on "Downgrade to: 5gb", I can then only hit the cancel button at the bottom.  The Done/submit button is not highlighted/not clickable.  So I have to cancel and I'm brought back to the previous screen.  It shows my plan ending on 10/18/16.  Do I have to wait till after that date?  Please help with step by step instructions.  Thks.