The same medium size may differ in size between a Japanese medium size and a medium size in other countries/regions because they are labeled based on different standards. Also, sizes may differ depending on the brand even if they are the same size. As a general rule, items that have already been purchased cannot be returned, but you should bring the item and the receipt of purchase to the store where you purchased it and ask if you can have it exchanged. Please note that if the product tag is cut off, the product is considered to have been used and cannot be exchanged.