Replacing ducts would be a tall task. They are all joined together, there are corners and jogs etc. Existing ones likely have some kind of duct / foil tape sealing them. They will be attached to the floor in various places.
Ducts are all installed while the unit is being built, prior to assembly of floor sheeting and more.
Anything can be done, but you'd have to open up the floor to access them. "Pulling" the ducts is not an option.
IMO, the best option would be to clean the existing ducts. Get in there with some kind of flexible snake with a cloth on the end, wet with a cleaner.
You could even remove the furnace, take it apart and thoroughly clean everything.
Spiral round flexible pipe is a great dirt trap. They are full of ridges inside and air will not flow smoothly.
Have a look at the Floor section of my rebuild site, link in sig. It shows one example of heat ducts. There are many other ways they do it.