if you're under 18, they're legally responsible for you, so you need to tell them. don't jump up and announce it though, wait for the right moment. try to gather as much information as you can, such as books [better if your library carries them] links to websites, pamphlets, and try to type up information, highlighting the key points.
when you feel the time is right, ask your parents if they could sit down because you have something to tell them. ask them to listen before responding. sit them down and calmly explain your faith to them, it's morals, beliefs, the fact there's no devil, and why you have chosen the new path. show them the pages and books, and ask them to read them over. be calm, don't be demanding, and even if they say no, don't fly off the handle and start yelling with them. you'll have a greater chance of acceptance if you're calm.
if they do say no, you'll have to respect their wishes and stop studying magick. like i said, until you're of legal age, your parents are responsible, once you turn 18, or 21 or whatever age it is for you, then you can return. Paganism teaches that if the path is right for you, you will return to it. it may seem like a long time to wait now, but it really isn't. in the mean time, you could take up gardening, study herbs, cook, make candles, study mythology, history, genealogy, astrology, meditation, yoga, and a slew of things that won't seem to have a magical element.