You can't edit a user profile's email address directly. To switch, invite the new address as a new user, then sign in from there.
Invite the new email. Signed in with your current account, invite the new address as a user and assign it the role you need (for example, Super Admin).
Sign out of your current session, or open the invitation in a private browsing window.
Accept the invitation. Open the invitation email sent to the new address and follow the link to finish setting up the profile.
Remove the old profile (optional). Once you're signed in on the new email, deactivate or delete the old user to keep your team list tidy.
Sign out before you open the invitation link. While you are still signed in, the link signs you back in as your current user, or tells you it has already been used.
If the invitation link does not work
If the link keeps signing you in as your old user, or you see “We couldn’t find this link. It may have already been used. Ask for a new one.”:
Sign out of Adfin first, or open the link in a private browsing window.
If it still will not open, go to Settings then Team, remove the invited user and invite them again. That issues a fresh link.
When you accept, sign up with your email address and a new password. Please do not complete any "set up your organisation" steps, as that creates a separate account rather than adding you to this one.