replacement of transmission speed sensor

I need to replace my speed sensor and was wondering if anyone could tell me how to do that on my own.

Year and engine type ? Basically, on top of transmission, sandwitched between engine and rack and pinion, near right (passenger side) half shaft. . Unless it is damaged by external forces , this sensor is quite sturdy and rarely degrades in performance. Any detail on the symtoms that lead to that change?
SIgnal from the speed sensor is processed by the speed sensor buffer, on a bracket behind the glove box compartment (90-96...may vary with other year model).

Year and engine type ? Basically, on top of transmission, sandwitched between engine and rack and pinion, near right (passenger side) half shaft. . Unless it is damaged by external forces , this sensor is quite sturdy and rarely degrades in performance. Any detail on the symtoms that lead to that change?
SIgnal from the speed sensor is processed by the speed sensor buffer, on a bracket behind the glove box compartment (90-96...may vary with other year model).

Hi, LMP-

Remember my reverse problem? It is solved now after changing it with a reconditioned unit...thanks for the advices since I found them very helpful.
But just after I had it changed, I faced a problem regarding my tachometer. It is reading less than my actual speed now,i.e. 60 km/hr instead of 100 km/hr.Any adjustment required?

Please, may I have your valuable advice? Here's the details-

Make: Pontiac Trans Sport 3.1L 3-speed auto
Type: 125c

Regards,
White Zorro