Units set up

I hv Blender 2.45.I wanna find out where is unit set up???:confused:help me

Why are you using 2.45?
1 unit = 1 blender unit. This can be whatever you want it to be.
The only important reason to use 1 blender unit = 1 metre is for things like physics simulations.

Thank, i m trying to create a track for VDrift using blender . So i want know can we change blender unit to kilometers , if we can, how? I am unable to understand of measurements of objects in blender.i had been using 3ds Max.I can find customize -->units setup in 3ds max.but i cant find such a thing in blender.,help me