I registered my Stack Overflow account using the Stack Exchange OpenID provider. I later changed my e-mail, but I cannot change the e-mail address associated with my OpenID for some reason. Why is that, and how do I change it? I logged in to Stack Exchange and it lets me change my password, but never my e-mail.
You cannot change the e-mail address attached to your openid.stackexchange account, by design.
If you've lost access to the e-mail you registered with initially, create a new openid.stackexchange account and either add it to your Stack Overflow account (via your profile page, if you're still logged in) or create a new Stack Overflow account and email us via the Contact link so we can merge the two accounts.