I don't believe in sugar-coating or blowing smoke, so I'll just be blunt as you're old enough to take it.  Unless your family is just very different from the typical JW family I would not get my hopes up of figuring out a way to tell them that will make them be supportive of you.  I know it sounds harsh, but we all know it's true that most JWs are too well trained to be able to think with their own rational thoughts about this sort of thing.

You're obviously going to have to be honest at some point unless you're planning on packing your bags and running out when nobody is around (and I would not recommend that).  Whatever you do, just make sure you have all your ducks in a row so if they come down on you hard for wanting to lead a normal life you aren't left out in the cold with nowhere to go.

Blood fractions?  Shunning family and friends?  "Stay alive in '75"?  Condemning the UN as evil and then joining it?  Shielding pedophiles?  1914 "overlapping generations"?  All the false prophecies?  Seriously??  Who could support this JW stuff without feeling like a total disgrace to Christianity?