You can downgrade, that is, switch from a higher priced plan to a lower priced one at anytime. In this case, your old (already paid) plan will remain valid until its initial expiration date. From this date on the payment for a new plan will be due. On the same day, the running surveys that exceed the quota of the new plan will be stopped based on the FIFO principle (First In – First Out): the surveys that were started first are stopped first until the number of active surveys allowed in the new plan has been reached.
