First, your character can remain tiefling, since you obviously earned at least one XP before the cut-off date to be grandfathered. Retraining/rebuilding other things won't require you to change your race.
If you haven't played the character yet at level 2, you still have the option to do a complete rebuild, changing absolutely anything you want about the character. If you have played it at level 2, here's the relevant text from the Society Unchained blog:
Society Unchained wrote:
In fact, we're so excited about these classes that we're announcing a one-time limited rebuild to anyone with one or more levels in these classes, allowing those characters to switch any levels in the four classes to their unchained version at no cost. This includes the automatic retraining of any rage powers or rogue talents, as well as the free retraining and selling at full cost of any feats, items, and other character options that no long function properly due to the unchained classes features. For example, a rogue automatically gains the ability to add her Dexterity bonus to damage, so she could sell back her +1 agile rapier at full price. Likewise, a barbarian with the Raging Vitality feat would no longer benefit from its increased Constitution bonus, so she could retrain that feat for free. Much like when we have offered free faction changes in the past, you'll need to take advantage of this opportunity before you play the character after April 29, 2015.
Since the unchained rogue qualifies for all the archetypes that the chained rogue has, the limited rebuild wouldn't let you add/remove archetypes; unless you bought an agile weapon (pretty unlikely at level 2), I can't really imagine much you could change.
