Chromebooks are powered by ChromeOS, an operating system developed by Google. While ChromeOS lets you browse your device as a guest, you'll need a Google account if you'd like to sync your data and access Google services. Since you access your Chromebook using a Google account, your Google account password is also your Chromebook's password.
How to Change Your Password on a Chromebook
Your Chromebook's password is the same as your Google account's password. Here's how you can change it on a Chromebook.