What you need.

A screw driver. and  an electrostatic band as shown below.

Installing a computer PSU

With a screw driver gently remove all the screws from the back of the unit. Carefully unplug all the power cables from the board and the drives. With one hand guiding the cables pull the unit out from the back of the case as shown in fig 19.

Installing a new unit is exactly the reverse of removing the unit.Gently install the power source unit as show in  FIG 20.

FIG 19.                                                                              

FIG. 20

FIG 21.