I have two line, the main one#1 is on second floor and the second one#2 is on the first floor, I want to disconnerct the #2 and the telephone company said I need to rewire the phone so I can use the Maine line#1 to first floor. How can I rewire it?

Hard to say exactly, but one possibility is this:

The lines are wired in the NID outside. You'll see a test jack. Plug in a phone and determine which line is which by whatever method you can come up with.

Then transfer the disconnected lines wires, red/green screws to the other red/green screws keeping the colors the same. Whatever color wire that was on a red screw goes to a red screw.

There are other possibilities, but this seems more likely.