Under normal circumstances, you can't completely respec your character in Torchlight 2. At best, you can redo a few things. Maybe you'd really like to respec though–as colleague Rowan Kaiser puts it, it's likely that your first character in Torchlight 2 is "wrong." Thankfully, crafty modders are here to save the day.
From site overlord Ian Miles Cheong comes the discovery of this Runic Games Fansite post, which has a download that allows you to respec. The instructions:
!!! CLEAR YOUR SHARED STASH !!!
!!! BACKUP YOUR SAVES !!!
Located here:
C:\Users\Username\Documents\My Games\Runic Games\Torchlight 2\save\RandomNumbers
Then extract the zip to this folder. Now you have shared stash full of respec potions.
Does NOT mark you as CHEATER
EDIT: This only refunds skill points.
The site suggests turning off Steam Cloud if you have any problems. Happy respec-ing!