I have two 'sick' urges, how do I throw them off?

The first one is to seduce a young girl of about 10-12 (I am 17). I know this is wrong but I just can't help it. Whenever I see a girl of that age swimming in a pool with no bikini top on I can't resist staring. The second is to see my pretty sister naked. I am not gonna lie to myself my sister is hot and I have had dreams in the past when I have seen her naked (17/06 being the latest one) and I have even masturbated to her I the past. How can I throw these 'sick' urges off? This is a serious question BTW.