is it difficult to change the tire sensors in the pontiac grand am 1990?

This is a follow up to another one of my questions, every other problem is been solved but the "BREAK" light is still
on now i know its the sensors but my questions are... where exactly are the tore sensors?  is it easy to do it at
home? or should i take it to a mechanic? also the "ABS" light is on as well.