There r two methods by which u can get +5V to -5V.
One is just reverse the polarity i.e Connect postive of ur circuit to ground of the supply and ground of ur circuit to +ve of the supply
Second one is u can use IC regulator 7905 to reverse the polarity
The 7905 regulator can only regulate a negative power supply, it can not generate -5 from +5, you can connect it in the gnd side having as reference the positive line (you also need more than 5v because of the voltage drop) but this is still using the first way you have described in which you reverse the positive line with the gnd, this is not true -5v with respect to the gnd.