Hi
This is what i have read but have not tried yet, will have to do this on our 2004 ulysse
1 Disconnect battery and WAIT ONE HOUR to discharge air bag from any static current or electricity.
2 Underside of steering wheel there is some cut outs place small slotted screw driver to release clips or similar tool, horn section of steering wheel should now release.
3 Air bag is held by three torx bolt undo these very carefully, remove air bag and places inside plastic bag and place somewhere safe.
4 Make sure wheels are aligned in a straight line or steering wheel is in correct position, undo center bolt 24mm socket I think and remove steering wheel.
5 This information I have read was on the fiat forum in the stilo section, so may not be 100% right for the Fiat ulysse but should be of some help
Best of luck.