I know the problem on my transmission, the solenoid needs to be replaced

my mechanic said there are 3 solenoids in the tranny but is not sure if they are easily accessible, eg from the fluid pan , or does the whole thing have to be dropped and opened up. he said he will change all 3 so there wont be a chance of changing the wrong one or if there is more than 1 problem. he wants to know the location of the solenoids. appreciate your help.