Prevent someone else from using my iCloud account?
To summarize what you should do in one single answer:


Change the rescue email associated with the account. You can do this by going to https://appleid.apple.com/ and clicking on Manage My Apple ID, logging in, and then making sure all the email addresses listed in Name, ID and Email Addresses section of your account are email addresses that only you have the passwords to access. In particular, the Primary Email Address associated with the account should be an email address that you and you alone control.





Under the Password and Security section in the Manage My Apple ID site, change your password. Do this after you change the email addresses on the account so you don't accidentally lock yourself out.


While you're in there, you should make sure your mailing addresses and phone number are also assigned to identities that belong to you and you alone.