Was wondering how to replace a 2 prong receptacle with a 3 prong one. There is no ground wire running to the box and it is housed in a metal box. The receptacle is downstairs, where I plug in my dj equipment. The house is an older house built iin the 60's.

The best way to do this is to replace the old 2-hole receptacle with a Ground Fault Circiut Interupter (GFCI) style of receptacle. Here are some quick instructions:
How to - Install a GFCI Outlet

Keep in mind, using a GFI will offer protection from a ground fault, however, it does not create an equipment ground, and any equipment that must have a solid equipment ground to operate, such as a surge suppressor, will not operate properly.

If you need a proper way to fix this circuit you need to run a new cable from the service panel to the receptacle.

Depending on on the amperage of the circuit (14/2 AWG for 15 amp. 12/2 AWG for a 20 amp circuit)and an equipment grounding conductor. If you are using NM (Romex) cable, the EGC is included inside the cable sheath.

A GFCI receptacle does no provide a grounded outlet as indicated by TK.