For me I got my dark sword from the item shop as a drop of course. And at the time I was rocking a legendary tier 8 sword with an enhancment of 61. Here a how I transfer: Click transfer upgrade on Tier 8 sword with 61 enhancement. Step two on that same screen I click the sword I want to transfer too example my unique dark sword . Step three click the ok button to finalize the transfer. Step four look at tier 8 sword and dark sword to make sure it has transfered the tier 8 enhancement to the dark sword. If so great.