Go to the official Minecraft site,(http://www.minecraft.net/) and log in. Once you have logged in, the "Profile" option becomes available, next to "Help" near the top of the page. Click on "Profile". (I haven't done this in awhile, but I'm sure it will work.) Click on "Choose File" and download the skin you need. Your not done quite yet though, in order to solidify the transfer of the file, click "Upload Image" and it will officially become your skin. I advise getting on Minecraft to make sure it worked. If not, curse my name and go watch this video: Just copy and paste the site name to your search bar.