This documentation introduces How To Reboot Or Select Boot Device A KVM/VPS On Rapid.Space NoVNC Interface.
You can refer to
to connect to your VM via VNC.
You are supposed to restart your VM to install a new operating system:
Press the number of your favorite boot device. Please follow the default US keyboard to input number, For instance, press 3 without shift if you are using French Keyboard.
As the screenshot, for example, you may press 3 to enter the installation guide of Windows OS