The only thing you need to do is delete the device from your account settings...but if you do buy a generation 2 I would install it first (before removing the old controller from your account) since we have added the ability to copy device settings, zones, schedules, etc. from your gen 1 --> gen 2 at time of install.
BTW - Existing generation 1 users should get an email regarding our pass it on program. Discounted generation 2.
Here is information on how to remove the old controller from your account: