You have to cut into your main supply line, to do this you have to stop the water, so make sure the main valve is functioning, it may not be. You have to solder the pressure reducer in as well, unless you have plastic pipe, which would be easier.
It may be better to hire a plumber.
HOW DO i POST PICTURES HERE, so I can show you?
Anyway, in the basement, the main comes from fhe floor, then you have the "Main-key?" for the water, and at about 20 inches higher, the WPR (Water Pre... )....
This is probably a matter of CUTTING, DESOLDERING AND SOLDERING Copper pipe... come let's tald about this people