Don't know if this will help, it's how to deactivate McAfee licences so may be the same for BTNetprotect. The other thing is just to keep installing on computers until they have all been used and when you try to put it on the 8th computer it my ether install or tell you what to do to get a licence.
However my advice and that of others on the forum would be to uninstall BTNetprotect. It can cause problems on some computers and is a resource hog. Do a search of the forum to see the problems. There are far better free antivirus programs available such as Avast Free and AVG Free.
If you do want to uninstall BTNetprotect use this guide and make sure you use the BTNetprotect/McAfee removal tool after you have restarted your computer.