It's the same you beat any other enemy. If the red orc is giving you trouble, try putting on different armor or weapons. Craft some strong health potions. Try some niche potions like the sleeping mist to get an edge. You got options.
How do I find the farmer Arthur? I've done the plum thief quest a while ago but I never actually found the farmer. I've been looking in the fields for days and been trying to make as much progress as I've could, but still no luck!