If your current broadband is delivered from overhead wires or an existing underground duct, they won’t need to dig up anything. They’ll more than likely reuse the existing route. (It's cheaper). For example, they’ll just push a new cable through the duct. If it is blocked or it is a wire buried Directly In the Ground, (known as DIG), then they may need to dig. If it is overhead that can also be done with fibre.
They will not lift carpets. All they will do is come through the wall and mount a new box on the wall, (called an ONT or Optical Network Terminal). This will require power and so needs to be within reach of a power point or an extension lead. It does not necessarily need to be where the old master phone socket is. The installer will discuss this with you, but he must regard it as do-able in the time allocated, (and be safe to do, of course).
The router then connects to that box instead of the old phone socket. Anything beyond that point, internal wiring, extensions etc., is your responsibility, (including any Wi-Fi setup), just as it is now.
