does it count if i send more than the 2 required Reference letters?
for example if i send 3 or 4 References ( all of them are academic ) would that give me better chances to be accepted ?

I added three reference letters because unexpectely I received my third referee´s letter on time, so I just added this one too because I liked it. I definitely would NOT send more than three though, otherwise you will annoy them. Actually sometimes they clearly state that they want only two and not more.

But to answer your question: The number of references will NOT increase your chances to be accepted. Two very good references will weigh much more than three "average" letters.

is there any difference between sending reference letters written by professors and written by assistant professors? do i have to take reference letters from professors whoes major is the same as the program i apply for? for example i will apply for international commercial law program so if i take a reference letter from a prof. whoes major is criminal law would it be acceptable?

Ideally speaking... a professor's letter is valued more than an assistant professor's. but sometimes your course may be taught by an assistant professor and you are often applying for the same course. in that case, frankly speaking...I think you should take a reference letter from the Assistant Professor whose area of expertise is the same as the one to which you are applying to.
In my case I took a letter from an assistant professor simply for the reason that he was teaching the same programme i was applying to and he could analyze my strengths in that particular discipline and strongly plead my case.

Some institutions put more weight in to references than others. I'd suggest that the greatest asset you have in your application is your previous academic performance from a University with a good reputation. Most application committees have a perception of which other law schools are strong for particular subjects, so assuming your undergraduate degree is either good, very good or excellent, the decision about your application may already have been made before references are fully considered.

Borderline cases can be helped a great deal by strong references, and in those cases, a really good recommendation is better than an average one from a well known professor.

What do you think about the reference letters written by alumnis from the school to which you are applying to? I have sent letters from alumnis who have supervised my work... I am not sure if it would have been better to submit academic letters...