You can do this in a few quick steps:

1. When you're logged in, you can go here to invite the correct email address: https://console.sift.com/account/team 
2. Sign up with the new email address.
3. Go back to https://console.sift.com/account/team signed in as your original email address and make the newly signed-up, correct user an Administrator (just click the '+' next to an email and then click 'edit' next to their Role to make them an Administrator).
4. Finally, go back to https://console.sift.com/account/team as the new, correct user and remove the old, incorrect email account.
5. Make sure your billing contact has updated to the new email: https://console.sift.com/account/billing (bottom of the page)