Adding an existing PC to a 3-license version of NIS

Hi,

 

we have a Toshiba notebook PC running the 3-license version of NIS.  This license is good until May 2009.  We also have a separate desktop PC running an older version of NIS, this license runs out in January 09.

 

We can't work out how to update the desktop PC so it's covered by a spare license from the Toshiba notebook. 

 

We have the product / license keys for both, we just can't work out how to do it.

 

Would we have to uninstall NIS on the desktop PC, then re-install?

 

Any guidance welcome ...

 

thanks,  Craig