can I swap transmissions

if i swap auto trans from 3 speed to 4 speed with overdrive, is it possible, do i need a new ecu(computer)? what else are involved i have a 131L 3 speed auto trans(no overdrive), i am planning to replace it with a 245L, a 4 speed with overdrive. will the old computer works is it possible to wire the 3 solenoid of 4 speed to the old computer ? what are involved, thanks to your help