If you feel a security threat or accidentally shared your Roku password with someone, use this method to change your Roku account credentials. You can also change the email address linked to your Roku account this way.

Go to theroku.com/password/resetand Sign in to your Roku account
In the Account Information section, click the Update button.
Enter your new password or email ID and click the Save Changes button.
Finally, your email ID or password will be changed.
You may need to change your password if someone gains access to your Roku account and makes purchases inappropriately. Also, sometimes you may have forgotten your password. In such cases, the method mentioned above is useful.