Well it will vary a little depending on the car. Look in the owners manual to get an exact amount. Typically they should be changed every couple years but it will depend on the car.
The fuel filter should change periodically according to your quality of fuel you used and the condition of your car. If you used the quality fuel then the life of the filter get high.
Generally they should be changed anually. Like air filters they can clog with debris and restrict the flow of fluids. Even the best filters can eventually clog and need replaced.