If you can log into the Openstreet map Openstreetmap website, pick My Settings on the dropdown menu top right, which shows you current email address and has a space for new email address. Enter the new one, save your settings, and I'm guessing you'll need to confirm the change from both old and new address.

If you can log into the Openstreet map website, pick My Settings on the dropdown menu top right, which shows you current email address and has a space for new email address. Enter the new one, save your settings, and I'm guessing you'll need to confirm the change from both old and new address.