Are rear-end gear swaps something i can do?

Are rear-end gear swaps something I can do or not? I want to get 3.73s in my a4 with stock 10 bolt. I noticed the gears and install kits dont cost very much but the companies i called so far want insane amounts to do the swap. Every place i call for anything wants insane amounts anymore lately so i end up doing most things myself and feel good doin it.

I know it probably wouldnt be easy but is this something I can do or not? Any recommendations on which gears i should get that will have decent strength and not any noise over stock? I am not interested in upgrading to a 12 bolt at this time. Any special tools i need?

btw, Is it true that 3.73s will improve my city mpg at all? I have 2.73s at the moment and get 25 highway but 12 city I hardly ever go on the highway though. Will it be good to do this swap for a street car with street tires or should i stay where im at?

I would recommend having a professional do it, and I will recommend Motive 3.73 gears. Doing it yourself is complicated and there's lots of room for expensive mistakes, plus the tools are somewhat expensive.

I doubt the gears will improve your gas mileage (they will reduce it on the highway a bit) but they will work fine in a daily driver.