Sure, you can change out parts and wires to upgrade a component, but, this is a process that involves listening to the results and perhaps back-tracking. The process involves "tuning" and "voicing" to fit your particular taste and to complement other components in the system. Any meaningful change in the sound resulting from a component change has the chance of improving or degrading the sound. It is not simply the case that a more expensive part, or one with a good reputation, will necessarily improve the particular system.
A local dealer that builds his own custom gear under his own brand name once had me listen to one of his amps. I am quite familiar with his amps, so I was expecting to hear something quite nice. I was reluctant, but, I ultimately told him that this particular amp sounded like crap. He smiled and explained that a customer sent it to another company that "upgrades" components and it was fitted with things like Blackgate coupling capacitors and fancy resistors; the customer was so unhappy with the sound that he was having the upgrades undone, which is why it was back at the dealer's shop.
One should approach this sort of upgrading as an experiment, and one should keep an open mind about the results. I see too many threads on these forums about things like tweaks that seem to always improve the sound--if they work, they change the sound, so how can the change always be an improvement? I suspect that at least some of the improvement is really expectation bias.