To add head and hands follow the 8 steps below

1. Download skin
2. Go to minecraft.novaskin.me
3. Go to top left and click open to open the skin file
4. On lower left of skin editor, click the "parts" bar
5. Click and make head under default layer
6. Click parts bar again and do left and right hands also on default layer (for trolls, humans, or cherubs)
7. (Ignore if not troll character) For troll wings. only default layer  to make wings
8. Click Apply on top right to apply to minecraft