How should I do this?

I just bough D-Worm COMBO Flavored Chewable for my dogs to eat. But I don't really know whether I should give them only once or many times. In the dosing table, they say that dogs weigh from 6.0 to 12.0 pounds should be given 1 and they don't say I should give more. So I think I only have to give them once, but I heard many other brands make us to give dogs twice or even three times. And btw, how long will the worms be gone and are they killed in the dog's stomach or it will be pushed out?