Only billing support can update your billing email. They'll need to verify your account ownership before making any changes. Email [email protected] for help with this.
Please be aware that your billing email address is only used to access the billing portal and receive invoices and receipts. If you use Midjourney on Discord, the login email you need to access your Discord account may be different. Midjourney support can't see your Discord login email, or help you change it. You can find more information about updating your Discord email address on their support site here. If you need more help with your Discord login, click the "Submit a request" link in the top right of that page to open a ticket with their support team.
If you can't log in to the Discord account your subscription is linked to, email [email protected], and we can help you move your subscription to a different account.