How do I shrink this extra large t shirt into a large t shirt size?

wash in hot water and use a dryer. Make sure to check the tag to see what the material of the shirt is. If it's 100% cotton, you'll have no problem shrinking it. If it has other synthetic materials in it, you may have a tougher time and have to repeat a couple times. Also check to see if it says "pre-shrunk". If it says this, then it's going to be difficult to shrink it anymore than what it is now.