Replacing existing 360

I have 2 daughters that will be using my norton 360 , One of my daughters bought  her own 360 . now i want to delete it so she can use my 360 . eg 3 users . problem is . i tried to unload her copy and re-install mine . but her laptop still says wrong key . and wont let me add my key ?

 

Probably a dumb question but hey ho . we cant all be computer whiss kids eh .

 

Any assistance would be very gratefully accepted

 

Many thanks

 

Johnny