Had it happen to me, and two friends, it broke. Welding is easy and you can make it stronger while you at it.
Just take out the seat, then pull all the hardware off it that keaps the uper/lowe attached (fairly self explanitory). The hard part is the head rests. I slide a slim jim like tool in next to the head rest to disengage the lock, but it is still a PITA. Can't tell you a good way to remove, it beyond that. Then you unzip at the botom of the back piece and slowly work the back off. You'll figure it out.
Then all that is left is to weld it or get it welded. While you at it, weld all the seams and add a couple of straps where it broke. The factory only spot welds the two shell halfs together and this makes them flimsy, leading to cracks and un-firm seating.
Then all thats left is getting it back together, its difficult, but if you take your time it will work. In the end you will have a more rigid seat than you did before, makes you think your car launches harder.