Note: You can only change your email address to one that is not already attached to an existing Patreon account. The change will not stick if you attempt to switch to one that already exists.
Step 1 - Select "Account Settings" from the drop-down on the top right and you'll be taken to your settings page. Once there you'll see your current email address that you signed up with.
Step 2 - Enter in your new email address and scroll down to click "Save Changes."
You will be sent an email confirming that a change of your email address has been made.