buy a head texture from market.
LINK It will cost you toricredits. Items are cheaper in market (200tc in shop)
Than go to your deactivated items. Head will be there.
DEACTIVE
If you see it there press edit button. A page will appear. Select the file you want to use. Press upload.
Than go to deactivated again. You will see your head there. now press activate. It will appear ingame