One of the big differences between Torchlight II and Diablo III is that in Torchlight II, it's much more difficult to re-spec your character and choose new skills.
You can visit a vendor in town to undo your last three skill upgrades, but past that, you're probably stuck with the options you've got. Choose well!
However, there is a re-spec potion in the game that lets you totally overhaul your character, even at a high level. But that potion is rare, and so it's difficult to find.
Thankfully, there's this workaround, uploaded to YouTube by MaguzEx. It's a hack, really, not a mod — you'll have to download a file and drop it into your Torchlight II save game folder. After that, the potions will magically appear in your shared stash, and you can re-spec to your heart's content.
Not bad. Maybe it's time to find out how my Embermage would do if she was more into lightning.
Torchlight II Hack Allows You to Reset Skills Infinitely: Respec My Dodge Mastery [Technabob via Nibblehacker, YouTube video by MaguzEX]