Slide the drivers seat back & wind down drivers side window and then disconnect the negative terminal on the battery. Drop steering wheel down and prise of the horn/air bag cover, stubby screwdriver helps.
You should now see the small torx screws holding the blanks on. Remove these and pop off the blanks and replace with new buttons and connect and tidy up the flat connection wires., clip the horn/air bag cover back on and reconnect battery. Start the car leaning thru the window, just in case air bag was to deploy, take it for a drive and any warning lights should reset themselves.
That's as much as I remember, there should be a few more detailed guides online if you do a search. I'm no expert BTW.