Change your Apple ID 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 Apple features and services that require an Apple ID, you are asked to sign in with your new Apple ID password. See the Apple Support article Where can I use my Apple ID? If you use your iCloud Mail account with an email app other than Mail on an iOS device, iPadOS device, or Mac, 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. See the Apple Support article Use a passcode with your iPhone, iPad, or iPod touch.