Step1 Check to make sure that your shirt is not "preshrunk," as there is little you can do in this situation to get the garment any smaller. Step2 Wash your shirt in a washing machine. For maximum shrinkage, use the highest possible temperature suitable for the shirt. Since it is more of the tumbling action of a washing machine, rather than the hot water that causes garments to shrink, check the care instructions on your garment to see if there are any limitations to what you can do with it. Hotter water does contribute to the effort, but it is not necessary if your garment instructions disallow hot water. Step3 Put the shirt in the dryer at the highest temperature possible. Leave the garment in the dryer longer than you usually do. Step4 Wash the shirt again, if it is not small enough. After it has gone through the full cycle, instead of putting it in the dryer, iron it. Iron the shirt at a high temperature until it is completely dry. Check the size again.