Place the pants with other clothing that needs washing in your washing machine. Add your regular detergent and a capl of fabric softener.
Wash the clothes in warm water. Washing the pants will remove any starch that may have been applied to the pants in the factory. The fabric softener will also help soften the pants.
Dry the pants in a clothes dryer on the warm setting. Use dryer balls, which are bumpy balls made to soften and fluff clothes in the dryer, to further help soften the pants. If the pants are still too stiff when you remove them from the dryer, repeat the washing and drying process.