Something that's been changed or revised is amended. An amended version of your English paper has been rewritten or edited in some way.
An amended piece of writing is fixed, and an amended opinion is improved in some way. An amended speech might be modified so it's more focused than it was, and an amended viewpoint has shifted in some way. You'll often hear about amended laws or ordinances — these have also been changed, usually to make sure they're fair. You could even say that the US Constitution is an amended document, as it's been altered by many amendments over the years.