From the web app

• Click on the profile picture in the top right corner of the page
• Click on the settings link
• Find the click on the Password tab
• Enter your current and new password and click save changes

From the mobile app

• Open the app and click the menu icon in the top right corner.
• Click on Settings and go to Security  in the list.
• Click on the Change Password option
• Enter your current and new password and click Change Password button