Article in English: Wear your jeans like you normally would. Try to zip and button them up, if possible, as that will help stretch them out farther. You may want to do this without underwear, as you'll be getting in the bath with the jeans on. The water will help the jean fibers relax while your body will do the actual stretching. Fill the bathtub with warm water. Don't use hot, and don't add soap or bubble bath to the water. Just use straight water. Make it warm enough to feel comfortable.  Hot water can cause the jeans to shrink. Don't use soap because then you'll need to rinse them out thoroughly. Sink down into the bath while wearing your jeans. It may feel a little weird, but it's an easy way to stretch them out! Make sure the waistband is completely submerged underwater. You can achieve the same effect by just wearing the jeans as you normally would without water, but it will take longer. Let the jeans soak for a good while with you in the bath. Try expanding your stomach or bending at the waist to help stretch out the waistband in the particular. Get out when the water cools down. Shake as much water out of the jeans as you can, but don't stick the jeans in the dryer, as that will just make them shrink up again. Lay them on a towel or drying rack, and leave them overnight to dry.  If you want to speed up the process a little, you can place them in the washer on the spin cycle, but don't let them go through a rinse cycle. You can also hang them up outside to dry on a clothesline.

Summary in Chinese:
像平常一样，穿上牛仔裤。 洗一个温水澡。 穿着牛仔裤跳进浴缸。 坐10-15分钟。 平铺牛仔裤，晾干。