Here's how to transfer the ownership of your paid account to another user.
The steps you need to take depend on whether the new user has an InVision account and/or owns prototypes.
If the new user does not have an InVision account:
Click on your name in the top right corner of your dashboard, then click View Profile. Change the email in the profile from your email address to the new user’s email address and click Update Settings at the bottom. Then the new user can reset the password as needed.
If the new user has an account and does not own any prototypes:
The new user should go into their profile page and change the email address from their current one to another (can be another work or person email) and save at the bottom. Once completed, you can follow the steps above to move the prototype over.
If user has account and owns prototypes:
They need to transfer prototypes over to you first. Once done, they follow the steps in option 2 above and once that's completed you complete the final steps in option 1 above.