Help replace a 1994 hatch latch

[zoint]

The spring broke on the rear hatch latch of my son's 1994 celica. He said that the end of the spring snapped off.

Now the hatch does not lock. I know of a junked 1994 celica and can purchase a used latch. Can you tell me how to replace it? Is it easy to do? Can I use my old lock cylinder? Thanks in advance.