Hit Command-T and type "Account Preferences".

Hit the "Change" button next to your email (see image below).

Enter your new email and password in the pop up.

Click the email validation link sent to your new email address.

Sign out of Arc on all devices and then sign in with your new email 🎉

Sign Out of Arc. To do this, go to Arc > Sign Out in the Mac Menu Bar.

Open Arc.

Fill out your email in the Email field.

Click "Forgot your password?" on the Sign In screen (see below).

You'll receive an email with instructions on how to Reset your Password.

Using your new reset password, go back to the Arc Sign In screen and Sign In.

Start browsing!