Is this what you have?
If the wires are not damaged then they do not need to be replaced, they should be solid copper.
In our home the only wires that I have trouble with are ones in the ceilings. The heat from the lights breaks down the rubber insulation. I would concentrate more on running new circuits to places that you need more power, like bathrooms and kitchens.
Pulling wires through bx can be done but 3/12awg wires is a tight fit, and all bx ends need bushings in them.
This is all based on you having bx. If you have normal conduit it's a lot easier.