How do I mod my fan

I got a 120mm panaflo fan that was already modded to run slower, what wires do I switch to get it back running at full speed again. Right now the red wire is on the left and black is in middle. Thanks

Forgot to mention. my fan model is fba12g12h

You didn't mention at what speed it's running at now, which kinda helps, depending on how the hall-effect sensors are set up.
most modern fans have two sensors, which in turn control two seperate coils inside the fan. In order to help you correctly, i need to know how many coils are in the fan (i.e. 2, 4, etc.) if your fan has a speed sensor, and states at what speed it should be running at, then it only takes simple math to figure out. you can do this like so:
(example)
Original Fan Speed = 3600 rpm
Current Fan Speed = 1800 rpm
3600 x .50 = 1800 rpm
(p.s.; sorry if its too technical, but i spent some time as an electronics technician) LOL

The red wire from the fan connects to what wire on the PSU? Red or Yellow?

http://www.fishnet.me.uk/7volts.html
they have images so it's easier