Fighters can do it with their bonus feats:
Upon reaching 4th level, and every four levels thereafter (8th, 12th, and so on), a fighter can choose to learn a new bonus feat in place of a bonus feat he has already learned.
Inquisitors can do it with their teamwork feats:
As a standard action, the inquisitor can choose to learn a new bonus teamwork feat in place of the most recent bonus teamwork feat she has already learned.
That's it, though. There's no general retraining rules.
My question is did paizo publish anything about having the ability of retraining feats like what was is in D&D 3.5 PHB2? My group is only using Pathfinder stuff and wont do any conversions of 3.5 materials!
I don't know what was in PHB2 but the only source I've seen for retraining feats is with the Fighter bonus feats.
However, I'd rather have my players retrain a feat rather than make an entirely new character astonishingly similar to the last character with a couple different abilities. Same thing with spells or other abilities, especially if they realize they made a crippling mistake or have never used them. My players are excellent about not cheesing this kind of thing, though, so YMMV at other tables.
At 2nd level, a titan mauler may choose to wield a two-handed melee weapon in one hand with a –2 penalty on attack rolls while doing so. The weapon must be appropriately sized for her, and it is treated as one-handed when determining the effect of Power Attack, Strength bonus to damage, and the like.
Note that Jotungrip does not work with the Massive Weapons ability they also get.
What about a feat that lets you wield a 2 handed weapon with 1 hand with a penalty to attack or damage or something like that?
If your DM is comfortable inventing feats that can significantly increase character power, then he's free to do so at his table outside of PFS.
If you're looking for existing rules, the Barbarian Titan Mauler archetype has an ability called Jotungrip that lets you use a properly-sized two-handed weapon with one hand. It does not let you do so with oversized weapons, however.