Extending display to a second monitor

I have Zorin 16.2 Education installed on an HP EliteDesk computer, which has only a single VGA port. I attached a port splitter to HDMI/VGA, and I've connected an Acer monitor and a Philips screen. Currently, the display is duplicated on both screens with 1024x768 (4:3) resolution. (The Philips screen is much larger and wider, and can take a widescreen resolution.) I can't seem to find any way to 'extend' the display (so each screen shows different windows). I made sure the graphics driver is up to date (Mesa Intel® HD Graphics 4400 (HSW GT2)). Any ideas what I need to do? (I'm quite novice when it comes to Linux systems...) Thanks in advance for any help you can offer.

Gday @tdickinson ,
You will only get a copied/mirrored view From a single port. ( using splitters)

If your using an Adapter/Converter & get both( Screen 1 & screen 2),,then try toggling between " Extend & Duplicate", ( reboot after each change, then change back)

Another thing maybe,
Run an update, with both monitors plugged in.

It sounds like an old pc,
i assume the Phillip screen (TV) has HDMI !

Can you tell us, what is the pc/laptop?

Do you see both monitors showing in, Settings > Devices > Displays?

Have you tried "Fractional Scaling", setting's.

Have you tried using a usb Adapter/converter to HMDI for a 2nd Monitor?

You can have multi screens (like 3 or 4 as an example)But keep in mind of the capabilities of your pc.