As long as you stay within the same HC level as you were last year, you can always renew your current seats. But if you drop an HC level, you can't renew your seats and have to pick new seats.

It is distinctly possible that your new seats will still be available by the time it's your turn to pick, so it's not automatic that you will be guaranteed to be sitting somewhere else ... but anyone else could pick your seats if they so desire.