This is quite confusing to tell difference between male and female angelfish. You can get idea by looking at their body feature but this is not 100 percent valid until you wait for spawning time.
Generally it is observed that male angelfish have more rounded crown or area right above their eyes. Males grow faster as compared to females. Males have more fatty and robust body ascompared to female. Females have straighter line of their dorsal , or top fin , to their eyes. By observing their behaviour you can again get some idea of difference. Males show their papilla when the females are around.
Papilla : This is pencil point size pink organ which is located between ventral and anal fin of angelfish. Above picture is having both male and female.This is generally observed near the spawning period. The female will show bulge in this area when she is gravid that is carrying eggs. While the females papilla is more blunt and wider. During spawning females lays eggs on tilted flat surface and then males will touch the eggs with its papilla.
Note: If no males are present then 2 females may spawn together. So look for the size of papilla. If this happens then soon eggs will turn white. You can see the picture for more difference.