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.
Here you go (Pic by Pic)
Step 1 - Go to Minecraft.net and click "Log In"
Step 2 - Go ahead and sign in.
Step 3 - Click on "Profile".
Step 4 - Click on "Download the reference skin."
Step 5 - Right click on the image and choose "Save as..."
Step 6 - Save it where ever you like.
Step 7 - Let it download, should only take a couple seconds.
Step 8 - Click "Choose file"
Step 9 - Find the file and double click on it.
Step 10 - Click on "Upload image"
I hope this helped you! :smile.gif: