Remove whatever is on the can.
Boil it for 2-3 hours on medium heat. The water ALWAYS has to be above the can.
Once it's done let it cool down completely before opening it. I lead a sad life because my can opener broke 3 months ago and I haven't bought a new one. I poked a hole with a knife. Hence, the skewer.
There you have it. :)
I needed a loose and runny dulce de leche for what I was baking. But if you boil it for 2-3 hours longer, you'd get an even thicker, richer and denser dulce de leche. Either way, absolutely delicious.