Change your email or password

Both live in Settings, Account. Password: enter the current one and the new one. Other devices stay signed in. Email: the change is confirmed from the new address — a confirmation link arrives there, and the change happens when you click it. Until then the account stays on the old address. If you no longer control the old address, that is fine; the confirmation goes to the new one. You may also be asked to verify your email address before some actions, such as commenting. Verification is one mail with one link.