We need to know more than that.... What size tank are they in? What are the water parameters? (temp, ammonia, nitrite, nitrate) What do you feed them? How long have you had them? Any tankmates?
A pair of convicts should be housed in at least a 20 gallon. For breeding, a good temperature is 80-82F. Ammonia and nitrite should be zero, nitrate should be as low as possible (less than 40ppm is probably fine for cons. Feed them a good selection of frozen and live foods. Do 25-50% water changes every couple days with water that is a few degrees cooler than the tank.
Also, are you sure you have a pair? Or at least a male and female?
And lastly, have patience! It could take several months for them to settle in and breed!