iCloud: Change your iCloud password
Your iCloud password protects the privacy of the information (such as your email) stored in iCloud. Your password also protects your ability to locate or remotely erase your device using Find My iPhone. You should regularly change your iCloud password to protect your information. Your iCloud password is the password for the Apple ID you use to sign in to iCloud.
Change your iCloud (Apple ID) password
Go to the My Apple ID website (appleid.apple.com) and follow the instructions to reset your Apple ID password.
For more information, see the Apple Support article Apple ID: Changing your password.
After changing your iCloud password, make sure you update it on all your devices and in any email apps you use to get your iCloud email.
If you set up iCloud on your iPhone, iPad, or iPod touch, make sure to set up a passcode lock on your device for added security. (Go to Settings > Passcode or Touch ID & Passcode. If your device has iOS 5 or iOS 6, go to Settings > General > Passcode Lock.)