Jeans Don't Fit Anymore? 6 Hacks to Stretch and Shrink Your Denim 

Wash them in hot water.

If your jeans have gotten a little stretched out, just throw them in a standard wash cycle, but put it on the hottest setting. This method works best if your jeans are made of a denim that’s as close to 100% cotton as possible. And a word to the wise: Don’t use any fabric softener.

Put them in the dryer on a hot setting.

After you’re done washing them on a hot cycle, toss them in the dryer, and turn it to the hot setting. All the heat will constrict the fibers in the denim, making your jeans snugger than they were before.

Sew a small piece of elastic onto the back of the waistband.

If it’s the waistband of your jeans that is a little too loose, try this handy trick: Sew a six-inch piece of elastic from a fabric store into the inside of your waistband on the back. Follow this useful guide to the proper sewing technique, and watch the magic unfold.

Spray them with lukewarm water, then pull to stretch.

This trick is the easiest way to try to stretch out a pair of jeans that shrunk down. Spray them with lukewarm water, and then lay the jeans out on the floor. Stand on each leg of the jeans, bend down, and use your hands to manually pull and stretch the jeans while they are wet. Feel free to pull them in any and all directions, reapplying the lukewarm water as needed.

Sit in a warm bath while wearing the jeans.

This one might sound a little crazy, but it works. Put on the jeans that are too snug, fill a bath with warm water, and sit in it. The warm (not hot!) water will help loosen and stretch the threading a bit. You obviously need to do this one in advance, and allow the jeans to hang dry when you’re done.

Carefully remove the waistband.

This technique is a bit more advanced, but it’s great if you want to get crafty. Rip the side seams of your jeans about two to three inches down and then cut the waistband at the same place. You’ll then add a separate piece of denim (or some other material like leather) to expand the waist of your jeans. (This picture guide shows the process step by step!)