You can upgrade your account to a paid account, or move to the free plan anytime during the trial.
If you do not upgrade before the end of your free period, your account would be suspended. You would be able to visit Hiver and re-activate your account by upgrading within 7 days from the date of end of your trial. If your account is not upgraded by then, your account and all its data would be automatically deleted. You can also write to us to get the free plan in the 7 day period after your trial has expired.