to get a new player skin you need to open /pokemon/save/<save name>/player.dat
and find the line named Skin|
what comes after the vertical line is the name of the skin that corresponds to a file in /pokemon/content/textures/NPC/
so if you want the main hero you would put ethan or if you want silver you would put '4'
to create a sprite you need to put the images in the layout you have
make the background transparent
and then make it into a .xnb(find splints posts he should have a place for that and other tools in his signature)
also in my signature is a link to multiple npcs that you can download
they are in .xnb format but you there is also a folder with the .pngs that you can look at to see what they look like