How to upgrade Individual Developer Account to a Company Account?
The best manner to accomplish this is to contact Apple Developer Program Support directly. 

You can find their phone number and initiate a support ticket from this web page:


https://developer.apple.com/contact/


I have found them to be expert at getting you the information you need to effect a smooth and orderly transition and help you from registering incorrectly or having any assets trapped in limbo if you make the transition incorrectly.