Skins are textures placed on a player to change their appearance. Each skin is a rectangular image divided into areas that act as the surface area of the player. A skin must be the correct size (64x32 pixels) and cannot contain transparency.
It is only possible to change your skin if you have purchased the full version of Minecraft. To change your skin visit the preferences page and upload a skin image. Alternatively, you can press the ‘change’ button next to a skin on this site to remotely change your skin.