It is true that telling your parents you wish to quit studying (or that you wish to change your field of study to something you actually enjoy), won't be an easy task, but if approached/handled in the correct way it is not an undo-able one.
The first step would be to compile a list of reasons why college/university studies are not necessary for everyone in life to make a success (whilst also listing examples of such people who made a resounding success of their lives, without any formal education/training - Google search can help you with this).
Then the next step would be to compile a list of reasons why studying is not right for you personally. Once you have both lists it is time to plan the event in which you will be discussing your choice with your parents. This does not have to be an elaborate affair and should just be something simple (and private) such as a meal by either your home, or your parent's abode. Privacy and intimacy is key here, since you can never be 100% sure what their initial shock reaction is going to be like. Don't let this scare you though since around 70% of parents tend to take the news extremely well once it is initially broken to them, and even if your parents fall into the 30% category of parents that totally lose it, you are their child whom they love and eventually they will come around to the idea - Remember, once a wound is exposed it can begin to heal.
When the "breaking the news to my parents" day/event arrives, start off by explaining to your parents that you have thought long and hard about your decision and in the end you realised that quitting will be better for you. Explain to them that it will be a waste of their money (or your scholarship providers money) if you continue because you do not have a passion for what you are doing and therefore you are most certain you won't be able to make a success out of it one day as a career because of this reason. Go on to remind them that life is short and it does not help wasting valuable time on something if it makes you miserable. Then read them the list of reasons why studying is not right for you personally and the list of reasons why studying is not necessary for everyone in life to make a success. Once done you can finish off by naming the names of around fifty highly successful people who don't have any formal education or training (which you compiled earlier using Google). To completely round off the topic/conversation you could add something in the lines of; "Success comes from hard work and not academic training. If you enjoy something and are therefore compelled to work hard at it, you are more likely to make a success out of it than if you pursue something you hate and find no enjoyment in".
Your parents are bound to have a lot to say to you at his point but whichever way it goes just remember that after this whole dreaded discussion with them is over, you can begin to get your life back and the worst will be behind you. Don't feel discouraged if they (your parents) try and retaliate by threatening to make you pay them back for the money's they have already paid or worse, if they threaten to disown you. 85% of the time this is just the initial shock kicking in and in a few weeks they will recant their "threats/decisions". My advice to you for the 15% of cases where this doesn't happen is this - You have one life to live. You have to ultimately live it for yourself and not for others. Time wasted is time you can never get back and if people can't accept your choices and wish to cut you off due to them, then so be it, even if these people are your parents. If they truly love you, they will come around eventually. They had their lives and made their choices. Now is the time for them to trust you to make decisions for yourself as an adult who is over the age of 18. If you are forced to pay them their money back, then do it with pride, even if it takes you years to do this, at least you will have the knowledge that you don't owe anyone for anything and that your actions did not have an effect on anyone but yourself.
With this all being said, quitting is not a decision to be taken lightly. Be very sure about your actions before taking them. Take at least a semester to think about it long and hard and then only quit if your feelings have stayed the same all the time. If you have any doubts, rather make an appointment with a student counsellor or join a student support group to see if you cannot resolve any of your issues that way first. Many students tend to quit due to feeling overwhelmed or when they are battling to cope. They then convince themselves the real reason for quitting is due to them not having a like or a passion for what they are doing, or simply that university/college is not for them. Be 100% sure of your reasons and also be sure of how you are going to feel once you have quit. If you feel you are going to have any type of regrets, then maybe you are being too hasty.
Take care and good luck in your choices. I hope my suggestions can help some of you out there.
P.S - If anyone has any stories to share with us regarding how they told their parents they were going to quit, pls share these with us in the comments section, as I am sure many students will find help in these.