Help replace front & rear differential fluid

Kia Sorento EX 4x4 2003. 30,000 miles.
Can I replace front & rear differential fluids my self with the help of my car mechanic or should I take the car to the dealer?
The Dealership will charge a lot more money (but of course it will be worth it if done correctly) I don’t feel comfortable with my dealership mechanics. Once they tried to charge me for fixing items which were under warranty. I also still have that kicking noise when I let go of the brake pedal. Dealership ship said they have no idea what I am taking about after they took the car for a ride.
If I can’t see what they are doing then I want do fix it my self.

Any way I can’t seem to find any info on how to replace front & rear differential fluids
my self.

Any info will be appreciated.

I would take it to the dealer. You may risk voiding your warranty if you do it yourself. They shouldn't charge that much just to change that fluid. How often does the owner's manual suggest to replace the differential fluid?

Thanks,
I did just that called a different dealership; they were very nice & professional. Set a date on October 28 to bring the car in to get the work done.