Hi Darvel,
You need not to uninstall Captivate 7 in order to use Captivate 8. You can install Captivate 8 also along with Captivate 7 and use both of them. In order to upgrade to Captivate 8 you just need to download Captivate 8 from the link given below and use your Adobe Id and password to install it .
https://www.adobe.com/cfusion/tdrc/index.cfm?product=captivate
If you face any issue please contact us on chat by using the :- Contact Customer Care and we will help you further.
Regards,
Rajeev.