Question

your friend has fallen into bad company he is spending more and more time with these new friends and drifting away from studies with your partner discuss the problem and decide how you could help your friend what could be some other ways to reach solution

Answer 1

You should advice your friend and tell him what is good and what is bad for him
you should make him realize the consequences of this bad company
you should  explain him with examples and practically 

Answer 2

First of all explain him/her properly and politely that how his new companies are harming him.If he doesnt understand you then also try and report his parents about his changed habits.