How to upgrade my lighting situation?

You first step shouldn't be advice by education. You need to learn lighting. It doesn't matter whether you are using available light, a flashlight, or a shoe mount flash. From that foundation, you can better decide what you need in order to achieve the results you would like. Arguably one of the better books for understanding how light works is "Light: the Science and Magic". Strobist.com is a good place to start learning about off-camera flash in particular:

http://strobist.blogspot.com/2006/03/lighting-101.html

And Kelby Training has several lighting and equipment tutorials, but it isn't free:

http://kelbytraining.com