For active direct iRacing accounts you can change your email address by logging into https://members-ng.iracing.com/ and click on your helmet, then click Account.
Once on the Account Page, click the Change My Email Address button and follow the rest of the online instructions.
If the account is inactive, you can still do this by logging into https://members.iracing.com/membersite/ and click the My Account button at the top of the 'Your Subscription Has Expired' page:
Please know that this option is not yet available in the UI or within the iRacing account section for Steam accounts.
If you have a Steam account, please reach out to Support@iRacing.com for further help to update your email address.