Hi there, welcome after a while. I’m here with easy steps to connect Virtual Private Server installed with Ubuntu 18.04 in Windows Operating System by using Remote Desktop Connection.
You shall use Putty and connect to your VPS server. Your server credentials are supposed to be provided by VPS service providers.

You shall use the SSH command as well.
ssh username@your_server_ip
After logging into your VPS use the following SSH commands to setup remote desktop connection.
1. Update the repositories you just added sudo apt-get update 2.Upgrade repositories sudo apt-get upgrade ( Y/N ) Click Y. 3.Install Ubuntu sudo apt-get install ubuntu-desktop ( Y/N ) Click Y. 4.Install xRDP. FYI, XRDP is free and open-source implementation of Microsoft RDP server that enables operating systems other than Microsoft Windows to provide a fully functional RDP-compatible remote desktop experience. sudo apt-get install xrdp ( Y/N ) Click Y. 5. Install Xfce. FYI, Xfce is a lightweight desktop environment for UNIX-like operating systems. It aims to be fast and low on system resources, while still being visually appealing and user friendly. sudo apt-get install xfce4 ( Y/N ) Click Y. 6. Check remote desktop using xfce echo xfce4-session >~/.xsession 7.sudo service xrdp restart?
Now it’s time to connect to your server by launching the Remote Desktop Connection application and input your hostname or IP over there. Note that you shall experience some security warning if it’s the first time you’re using it.

You’re all done, congratulations!!!
Any problems? Do let me know if we can help in the comment section below. Thanks!