How do you respec in Mass Effect 2?

Solution 1:

To reassign points to your powers, you'll need to use the Retrain Powers upgrade in the Research Terminal, which can be found in the Research Lab on the second deck of the Normandy. In the Research Terminal menu, it's located under the Prototypes research category with the following description:

Advanced training allows Shepard to re-allocate points to powers. No additional points are granted.

Shepard can complete this research project multiple times. Each time the project is completed, all points spent in powers will be reset. Access the squad menu to re-spend points immediately after completing this research project.

This upgrade becomes available after you complete the mission on Horizon, and costs 2500 Element Zero per use.

As yx. mentions, you can also access this upgrade at the Research Terminal in the Shadow Broker base after completing the mission associated with the Shadow Broker DLC. The terminal will be to the right and up the stairs on subsequent revisits, and operates the same as the one on the Normandy.

MBraedley's note in the comments is also correct. In the Shadow Broker's base, to the left, you'll find the Advanced Training* console. This console allows you to redistribute the ability points of your squadmates much like Retrain Powers can be used on Shepard, at the cost of 1000 Element Zero a pop.

*This terminal is somewhat confusingly named, given that Shepard has his own Advanced Training option in the Research Terminal which performs a different function.

Solution 2:

The option to respec appears in your research terminal (in the room with Mordin) after the Horizon mission.

It will cost you 2500 element zero but you can use it as much as you want, and it only works for Shepard.

Apparently there's also a way to respec at a terminal in the Shadowbroker DLC, but I don't have it so I can't tell you where it is.

Solution 3:

You can reset your skill points with the Retrain Powers upgrade. It unlocks automatically after you complete the horizon mission. The upgrade costs 2 500 element zero to use, and you can use it multiple times. You do need to pay the 2 500 element zero every time.