Select the "Change" button located on the right side of any skin's detail page of your choice, you will then be brought to Minecraft.net, after logging in there, proceed to select "change" skin. When you enter game, your skin will be changed in-game.
Select the "Download" option, the skin's .png file will then be downloaded onto your computer, you can upload it manually onto http://minecraft.net/profile under "Change how you look in Minecraft" browse, and select the skin file you have just downloaded and select upload.
Select the "Download" button located on the right side of any skin's page of your choice, you will be prompted to save onto a directory in your computer of your choosing.
After entering any skin's page of your choice, select "Download", a new page will open on your mobile browser, tap and hold down on the image and select "Save Image" skin will be saved onto your mobile device. Go back to Minecraft PE, choose custom and select the skin you have just saved.