I guess the best you can do is start studying and do your best. You probably won't learn everything you don't know by tomorrow, so try your best to learn at least a few things pretty well (and pray this will be on your test).
To be honest if you do not know it now you will not know it during the exam. Your best bet is to simply read over the summary study guide that any class provides at the end of the term. Doing that will jog your memory, even a little bit. Go over the basic topics because that is what teachers focus on. Though generally speaking the last section of a course can have the most detailed questions because it should be the freshest material in your mind.
Oh and get a good nights sleep. Nothing gives a brain more fuel to work well than a good sleep.