iCloud: Change your iCloud password
Your Apple ID password protects the privacy of your information stored in iCloud, such as your email. Your password also protects your ability to locate or remotely erase your device using Find My iPhone. You should regularly change your password to protect your information.
The next time you use Where can I use my Apple ID?, you’ll be asked to sign in with your new Apple ID password. If you use your iCloud mail account with an email app other than Mail on an iOS device, a Mac, or on iCloud.com, change your password in that other app too.
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.)