Note: Now that most players are on Microsoft Secured Accounts (MSAs), basic actions such as changing one's email and password must be done through Microsoft Account settings instead of through Mojang settings.
To change the email address on a Mojang account, visit account.mojang.com/me/settings. You can either have instructions sent to your current address or if you don't have access to that email account, you can change it by passing a security challenge.
If you have registered for a Mojang account using the incorrect email address and have not made a purchase, you can re-register under the correct address.
If you have lost access to your Mojang account email address, we recommend contacting your email provider to regain access to the email account. This way, you can edit any settings associated with your Mojang account (including the Mojang account email address).
If you cannot change your Mojang account email, have your transaction ID or gift code available and contact Minecraft support.