Well, I just joined a gym again because I want to start lifting weights to tone up and build some strength. I do not want to bulk up a whole lot and I know to do more reps at lower weight. But how do you know how much weight is too much.

If the weight you are lifting is too much for you to life more than fifteen times...then it's too much.

I totally disagree. Women don't usually have the testosterone necessary to really get "bulky" so unless you suspect that you gain muscle very easily, then you want to aim for the 10-12 rep range, and as soon as that becomes too easy (the last rep is no longer a struggle) up the weight so that you are continually stressing the muscle. If you're not stressing it enough, it will not respond with strength improvements or tone.
The "light weight, high rep" method isn't good for much other than building endurance, which has its place, but won't efficiently help you with your goals.