Long time ago, when I bought this game, I set my payment method to Crysta & the period length to 90.
Now today, I want to change this 90 days to 180 (price reduction yes plz! ^^)
But when I click the 'Update' button, next to period length, I get this error:

・There are currently no active options.
If you have not added any options or all of your options have a status other than "continuous," you will be unable to update your payment method.
(Error code: 104)

So that means I can't change this period till the free trial period is over?
So I'm forced to pay for 90 first, before I can change it? Or is there an other way?