Sports jerseys have the colors of a particular team and often bear the specific numbers representing one particular player. There's no reason why you can't remove the numbers from a typical jersey if you've grown tired of them, are disenchanted with the player or want to replace them with new ones. Removing these numbers takes time and patience as you don't want to do anything that will damage the polyester fabric of the garment.
Sewn-on Numbers
Turn the jersey inside out. Slide the seam ripper under one of the stitches that attaches the numbers to the shirt.
Pull the seam ripper towards you, cutting out the thread. Continue in this fashion until you remove all the threads from all the numbers.
Turn the shirt right side out. Pull the numbers towards you once you've ripped out all the threads. Yank out any lingering threads in the garment.
Ironed-on Numbers
Turn on an iron to a high setting. Allow it to heat up.
Press the iron directly against the numbers. Move the iron back and forth, trying to keep the iron off the polyester of the shirt, but directly on the numbers. Your goal is to melt the glue beneath the numbers.
Grab the edges of the numbers and pull towards you. If you've adequately melted the glue the edges will start to peel off. Slowly peel off the entire numbers, being careful not to stretch the polyester shirt. You may need to apply more heat from your iron now and then.