How to I switch back to a DSL internet connection from a Broadband internet connection (through the cable co)?

I have a laptop, and my parents have a desktop with sbc DSL internet. I was using that internet before I moved away for college, and there I used an internet connection through our cable company via a router. Now I am back home for Christmas break and I would like to connect back on to their DSL, but I can't figure out how. Help! Thanks!