You can change your password by following the steps given below
Click on the settings button available on the left side menu or click the profile picture and choose it from the dropdown.
Click on Change Your Password
Enter your Current Password and your new Password twice and click change to update your password and click on cancel to discard and exit.
Make sure that you create a unique password to prevent someone from breaking into your account. Click here for a few tips for creating a password and keeping it safe