If you want to change the email address linked to your folk account, just follow these steps:
Log in to your workspace and then invite yourself with the new email you want to use for folk. Do this by going to settings > members > invite members.
Then make sure to share all your groups with this new member on your workspace
Log out and now log in with the new email to complete your account creation and join your existing workspace with the new email
Log out and log in again with your old email to change the owner of the account. Go to settings > members and make your new email the account owner of the workspace
Now you can log in with your new email and remove your old email. You're all set!