Every puppy has to stop nursing, and it doesn't require human intervention. As a puppy grows, his mother will eventually stop allowing him to nurse, because the sensation of his teeth clamping down around her teats is so unpleasant. In the wild, this is when he starts eating solid food in the form of prey. When the puppy and his mother are your pets, though, you can help facilitate the process by introducing solids yourself.
The Weaning Process
A mother dog starts to wean her young off of nursing when they are between 3 and 4 weeks old. When they are your pets, this is about the time you should gradually introduce a semi-solid, gruel-like form of food to the pups. It may take some encouragement on your part, like gently dipping the puppy's chin into the mixture to entice him, but over the next several weeks, he'll nurse less and less. Sometime between the age of 6 and 8 weeks, your puppy will be completely done with nursing and eating solid foods full-time.