Log into the website in question. Then go to your profile/settings on that site. Locate and make the changes you want.

jdcron said

I want to change my longin information to a different email and password.

Is that a question about a Firefox Account, like for the Sync service?

Of course it it is.

You can't directly change the email address that was used to create a Firefox Account.

See this to learn how to add a secondary email account. https://support.mozilla.org/en-US/kb/add-secondary-email-address-firefox-accounts

After that is successful you can switch the secondary email address to become the primary email address.

Doing that doesn't necessarily require a different password, but if you do change the Firefox Account password your Sync data will be deleted from the Sync server. So keep that in mind depending upon why you asked about this.