One of the most anticipated features in Diablo 3 is the Legendary item reforging system. Here’s what we know about this:
What Does Reforge Legendary Do in Diablo 3?
Reforging items can be done to increase their stats or to obtain Ancient (or even Primal) items, which are far more potent but also rarer than ordinary items.
One out of every ten items is considered Ancient, while one out of every 400 items is considered Primal.

Can You Upgrade Legendary Items in Diablo 3?
Any legendary weapon may be upgraded. As long as you have adequate crafting ingredients, you can use the “reforge legendary” formula in Kanai’s Cube to repeatedly recreate the item.
Therefore, you can reforge any legendary item you own until it becomes ancient.
Is Reforging Legendary Items the Best Way to Get Ancients in Diablo 3?
Although it’s pricey and will require you to harvest the raw materials, reforging is an effective way. You may combine reforging with these additional techniques [1].

- Rares can be upgraded in Kanai's cube (this still requires raws but not as many)
- Run a ton of Greater Rifts on the character you want to earn Ancients and Primals on (Primals won't spawn until you finish a Level 70 Solo)
- Spend your shards at Kadala on the item from a certain slot that you wish