If this is a pre-built, then chances are you won't be getting the 'extras' that are usually packed with the components if you were to buy parts yourself. I would pop into Wally World (or go to Amazon, Newegg, etc) and pick up the DVI/VGA adapter. That's what everyone that has an older VGA monitor uses. HDMI to VGA converters are expensive, undependable, and add an extra layer of signal distortion to the output. Plus, there's no need for such a thing in your situation.
Most R9-270X cards will have 2 x DVI ports, 1 x HDMI port, and a Display Port.
http://www.pcgameware.co.uk/images/MSI-270X-GAMING-OC-outputs.jpg
Check the system you bought to see if it has that arrangement of output ports.