Icloud uses your apple ID and password unlike every other apple application including contact and messages. All your apple devices works with one apple ID and loosing access to that ID means you will be locked out of your all apple devices. To reset the password you will need the email address you have registered with apple while making the ID and if you had activated two-step verification for your apple ID then you will also need the recovery key.

While it comes to resetting your password for security reasons and you have the password for your ID then you can simply do it by logging in to your ID. If you have forgot your password and want to recover it than you have to access apple support pages for further actions. To execute icloud password reset for security reasons process go to apple support webpage click on the “forgot apple ID and password” link and it will ask the security question associated with your ID. You can also select the “get an email” option to receive a email with a password reset link that you need to use to reset your password.