To change your password you need to navigate to your account page. To do this click on the person icon at the top of right side of the screen and select 'My Account'.

From the menus on the left select 'Change Password'. 

On the screen that appears input your current password and then type your desired new password into the 'New Password' and 'Confirm Password' boxes. 

To finish the process click the 'Change Password' button.