ANDY'S ANSWER: If you've never said anything before, it could be hard to bring it up, but the best way is to find a time when you know you will not be interruped and start out with "I have something I really need to talk to you about...."
You might find it easier to talk to just one of your parents at a time.
If there is no time at home where you can get that privacy, you might have to orchestrate a time for yourself like asking them to come for a walk with you. Head for a park or someplace that you could sit and talk, or just talk while you're walking. Make sure no one has to be back back for any specific time (like getting home to make supper or go to an appointment) to allow yourselves all the time you need to talk.