I can't help on a Kia and it's been years since I was swapping around stereos
But this should all be easy with the following to bear in mind:
An adaptor plug may be needed to connect a new standard wired stereo to the Kia wiring.
A fascia adaptor will deal with any size discrepancy between a Kia original stereo and a standard new stereo
Things will be as 'simple' as unlocking the original one from the bodywork, checking manuals and online for where the hidden clips and screws are
Then the new one is just plug and go
(If your current one is coded then write it down so you can sell it on or put it back later when you sell the car)
If you go for a 'letterbox' size stereo new then anything will fit based on the above options, if you want something more functional that fills the space of modern cars then it's still a matter of some common standards, but will fit or won't
Ask at a car shop or look for Kia forums
Halford's are pretty simple but bear in mind their 'fitting' is just a teenager in the shop unplugging your old one and plugging in the new one. Anything more complicated isn't for them
I used Halford's fitting once because it was free, they failed because he was confused by extra wires because of my amps etc
Telling him to just plug it in was a failure, (plug in the big plug, and plug in the amp out put plugs - just like they are plugged into my old one ...... ) he gave up and I plugged it in myself
