Did you just buy a shirt and realize after a second glance that it should be a size smaller? If the purchase is nonrefundable there are ways to shrink the shirt in the dryer. Make sure that the shirt is not already pre-shrunk, because it will be hard to reshrink the shirt. Some fabrics are easier to shrink, cotton being the easiest and nylon being one of the hardest.
Determine the probability of shrinkage for your shirt. If the shirt tag says pre-shrunk, it will be difficult to shrink the shirt once again. Also, check what fabric your shirt is made of. If your shirt is 100 percent cotton or has a high percentage of cotton, it should easily shrink. If your shirt is made of a synthetic fabric, such as nylon, it will be a bit harder to shrink. High heat can also ruin a synthetic fabric. Decide if you want to risk it.
Wet your shirt before you place it in the dryer. If you do not want to put your shirt in the washing machine, rinse it under warm water in the sink. Water facilitates the shrinking process.
Put your shirt in the dryer, dry it on a medium-high heat setting, and leave it in for the full cycle.
Remove your shirt from the dryer, and try it on for size.
Repeat this process if you want your shirt to be smaller.