Previous version gets overwritten when you install new version -- so you don't need to uninstall anything. Just install on top.
Previous license key is fine -- though it should not be asking you to put in a new license key if you already put in the old one, so check your about box and make sure it really does accept your license key.
As far as the deep forum section organization -- I hear ya, but there is no perfect way to do it -- too many at the top level and it becomes overwhelming.
