The weaning process starts when the kitten is 4 weeks of age.
Start by feeding it formula in a bowl. Do not leave the kittens unattended with the bowl at first! The kittens will run through the bowl and the dried milk on the fur and skin can cause ringworms and other skin and fur problems.
Then gradually introduce solid food. Moisten dry kitten food with formula or water. Read the labels! The dried Kitten food should contain at least 30% of Crude Protein. Much of what is sold in supermarkets is pure junk food and may not help your kitten thrive. Most canned cat foods will cause diarrhea and foul smelling stool.
Don't expect the kitten to be weaned overnight. As it eats more often from the bowl, reduce the bottle feedings.
Changes in diet or certain foods can cause diarrhea, so keep an eye on stools. Diarrhea can be life-threatening to a young kitten.