Change password
1. Log in to Sitecore, and on the Sitecore Launchpad, click Control Panel.
Or, click the Sitecore logo in the lower-left corner and click Control Panel:
2. In the Control Panel, in the My Settings section, click Change password.
3. In the Change Password dialog box, enter your current password and then enter and confirm your new password.
4. Click Change password.
From: https://doc.sitecore.com/developers/82/sitecore-experience-platform/en/change-your-sitecore-password.html