We have 8 dogs, most of them working dogs, and I do most of the medicating myself.
It depends on the type of worms they have. I use Pyrantel liquid wormer. It is available at Walmart in a small size, and at most feed stores in a larger bottle. Just follow the label directions. It doesn't work on all worms, so be sure that you are treating the correct kind.
Best of luck to you!