How can i trace back my ancestors?

I'm really interested in trying to found out about my ancestors. I know the names about 6 generations behind me which are about my grandparents grandparents on my mothers side. All of my family is from Colombia. I have first names and last names and I DO NOT want to pay. Most my family still lives in colombia and my grandma was the only one out of her eight siblings to immigrate into the us. How can I track down even more family maybe even get more information on my grandparents grandparents other children.