Q: I have followed the steps above but when I get to the screen to select a downgraded option, the  Done button is grayed out and won't let me select a new option. I see a lock up in top right-hand corner, but not sure how to unlock it.

If you are a former MobleMe user, the Done option isn't available to downgrade to the free 5GB plan because this will automatically happen at the end of September anyway.  If that's what you want to happen you don't need to do anything.

I'm not sure what would cause that.  Try calling the Apple online store (1-800-MY-APPLE in the U.S.).  They process icloud storage refunds so they may know something about this.

1. Choose Apple () menu > System Preferences, then click the iCloud icon.
2. Click the Manage button.
3. Click Change Storage Plan.
4. Click Downgrade Options.
5. Enter your Apple ID password, then click Manage.
6. Choose your current plan, then click Done.

(from http://support.apple.com/kb/HT5527 )