in general you can run
lshw -c video from a terminal to get all the basic info about your VGA, without knowing anything you can also run
lspci -n and paste the output at this page http://kmuto.jp/debian/hcl/ to get the name of the required module under a general Debian-like distribution like Ubuntu.
Keep in mind that some modules require additional configuration but usually Ubuntu automate all the tasks for you, but it's always a good thing to google a bit more about the module you are about to install under your system.
Also check di utility "additional driver" in your control panel for further tips.
for the same hardware several modules can be available, the site that i suggest usually display the one that are already available in the official repository, for example for an ATI VGA the site display the module
radeon but you can also use the proprietary driver that you can download from the AMD website.