Top tip from me as an "expert"...
Go and collect new battery, place in boot.
Drive home.
Disconnect old battery.
Go to boot and look confused as the boot won't open electronically.
Realise stupidity
Actually, make sure the car goes to 'sleep' after removing the ignition key there's a period of at least 5 minutes (possibly more) where the ECU is still busy and you don't want to disconnect the battery during this phase. I left mine about 30 mins just to be sure.
Also keep the windows fully closed, keep the doors unlocked, keep the key on you and not in the car. This is purely as a precaution you don't want something to throw a wobbly and lock the key inside the car etc.
I left my drivers window down and then had to 'teach' it the fully closed position again after changing the battery. I noticed if you leave the window closed you don't need to do this.
Other than this you'll only need to reset the clock, nothing else will be affected.