You can change the Windows VPS password from the panel by following the below options -
1. Go to your clients area > services > Select the server/Ip you want to change the password of.
2. After clicking on the 'Change Password' option, You will see the following screen and set password there.
3. After saving the New password you provided, You will see a confirmation message saying you have to reboot the server so your new provided password can work.
4. Now restart the server from the panel which may take up to a few minutes.
That is it. Have patience and let this server rebooted. You can now login into the server by using your new provided password.
If you need any assistance with this, please let us know/knock us.