ask them why they are against a puppy in the house.
and what can make them change their mind.

tell them why you like to keep a pet, and tell them all the procedure and way to take care the pet, in this case the puppy, you should know how to keep it if you are insisting to keep.

simple.score good results.study hard.do not make them angry.if u score high marks tell them to giv u a reward. say that u want a puppy and wont neglect it.that`s all