To change the password for your admin access, simply log in with your old password.
Go to, My Profile > My Account.
Alternatively, you can access your account settings from your admin dashboard.
On the left-hand side menu, go to Profile > Password.
Enter your 'Current Password', 'New Password' & 'Confirm Password' fields and click 'Update'.
Next, log out and log in again using your new password.
Also, watch the video on 'Changing Your Admin Password'