Disconnect the battery first, then wait maybe 10 minutes for the SRS capacitor
to discharge. No electric, no airbag discharge.

 It is actually very difficult to accidentally deploy an air bag unless you're
randomly probing wires with a multimeter or test light.
 Disconnect the battery negative terminal. It's good practice to let the vehicle sit
for about 1/2 hour for the SRS backup supply to discharge. Remove the bolts holding
the air bag to the wheel. Disconnect the electrical connector for the air bag and
remove it from the car. Lay the air bag face up in a safe place.
 If you are repairing something electrical, like checking the horn and cruise control
after you replace the wheel, it is ok to reconnect the battery with the air bag
removed. The SRS lamp will flash indicating a problem (obviously). Just disconnect the
battery for 1/2 hour prior to reinstalling the air bag.

Just disconnect the battery for a bunch of minutes and be careful.
Don't rush, it's easy -- you will say that when you finish.
Hank