Step 1: Login in your client area.
Step 2: Go to, My Products & Services and here all of your services will be listed.
Step 3: Open your VPS hosting Service.
Step 4: Now, scroll down and you will find the following. And select the "change password" to change the root password.
Step5: The following window will pop up to change the root password.
Step 6: Enter the New password and save it.
Note: If you don't find this option under your product & services. Kindly open a support ticket.
That's it !!