First of all, kudos to you for being determined to make yourself a better life even in the face of opposition. I hope that you find the internal strength to keep walking this path.
There are two possible reasons that I can see for your parents' opposition to your continuing education. Hopefully, it is just that they cannot see that higher education is an investment that pays big dividends later. I hope that it is your future which they are concerned with and not just their own, but either way, I think your best course is to try and show them the benefit with real numbers.
You didn't mention what course of studies you are pursuing (hopefully it is a lucrative one), but you might try googling for average salaries, comparing what you would make if you went out and got a job right away, and what you would make after college. Show them these figures. If you have any friends or family who have jobs similar to what you are targeting and who wouldn't mind telling you how much they are making, that might be an even stronger testimony than just numbers off a computer.
You also didn't mention who was paying for your education. If money is tight for your parents, it may be putting a great burden on them to pay the costs. Getting a part-time job would be harder on you, but it would ease the burden on them. And there are benefits if you can get job experience in your chosen field.
The second reason, and one which I am more hesitant to address, is that, because they never got a higher education, they may be afraid that you will look down on them, or leave them behind. I had a friend who was the first in her family to go to college. Her family not only stopped supporting her financially, but turned their backs on her, no longer informing her of family gatherings, talking about her behind her back, and telling her to her face that she was "getting above herself" and that she thought she was "too good for the family". Eventually, she couldn't take the pressure and the isolation so she quit school. I don't know what happened to her, as she never wrote me again.
This is a more delicate problem, yet it might be solved the same way as the first. Show your parents that they will still be a part of your life after you have finished your education. Share with them what you hope it will be like. Show them that you have thought out the details of your life (yes, I know, our lives do not always go the way we planned, yet it is important to make those plans), and show them how they contributed to this life. Parents need to feel their children's gratitude. They sacrifice much to raise children, and it warms their hearts to know that they are appreciated.
Expectations being different in America than many countries, and my husband and I have no thought that our children will support us financially in our old age, but once they are grown and independent, we hope that they will look back and appreciate what we have given them as they grew. And that they will at least be there for us emotionally when can no longer support ourselves.
If you can convince your parents that you have a good plan and are determined enough to succeed at it, and that you are grateful to them for giving you that opportunity, it may make them feel safe enough to stop pressuring you to change your plans. But if not, you must understand that it is you who must be responsible for deciding your life path. They made their own choices, as was their right, but you also have that right.