Your Ramp account is linked to the email address that you created it with. If you would like to change your email address, you will first need to contact Ramp support to deactivate your existing account. Once this is done, you can set up a brand new account using your new email address.
A couple of points to note. Firstly, you can only deactivate an existing account if you have verified your identity on that account. Secondly, Ramp has a strict "one-account-per-customer" policy. For users who don’t contact Ramp support to deactivate their old account, this can result in restricted access to one or both accounts.