Help with upgrading to new version using CD key

Hi guys: I just posted in another thread but just noticed its tagged "solved" so Im reposting.   I  have a 2007 NIS CD with key that is currently installed on Vista rigs that I want to upgrade to 2010 for free.  I talked with chat last night and someone named sreegreshnalkej or something told me in broken english whatever I wanted to hear, so Im a little unsure about doing this.  My subscription is still active for another 10 months and I have two computers on it that I want to upgrade.  Chat told me to download and install right over the 2007 version, but in the past, this ALWAYS led to disaster when 1 Norton tried to play with another.  Could you tell me how yous guys would do it?  These two laptops belong to my daughters and they are always away at college during renewal time, so I purchase another 2007 CD and then tell them the code to type in and voila, they are renewed without any troubles.  Will I be able to do this again  next year with a new 2010 CD key if we do this upgrade now?   Best Regards--JJ