Refresh the page and try again in a few minutes. Technical issues occur on most websites but correct themselves .If issue persists,contact a moderator by clicking ?, bottom right, and following instructions.
Best to be patient and renew a plan on the next renewal date to avoid issues like this. Click on "Change plan on next bill date" and everything should be fine. I used this method to change my plan and it was flawless. No mishaps. If this doesn't appeal to you, click on ?, bottom right, and follow instructions. A moderator should resolve the issue likely within several hours or a day.
I know that when you choose the plan you want you have to click [change plan now ]if its before your montly renewal date that you are trying to change your plan .if not the new plan will only be change on your montly renewal date.i hope this helps.