A lot of bad ports lock the framerate at something horrible like 30 regardless of whether you turn vsync off or on, but in most its possible to change it by editing a file somewhere or other as others have mentioned. Finding the right file and line can be a pain then, which is why you should visit
http://pcgamingwiki.com/wiki/Home
and search for whatever game you're having trouble with. If there is a way to unlock the framerate, there will probably be a step by step guide showing you how to do it. The website also has a bunch of fixes listed to common problems which aren't framerate related.
If that fails just google it. There is no failsafe method of unlocking the frame rate in every game out there.