Neither of the following procedures is difficult if you are patient and allow yourself adequate time. Don't rush the first time through the repair.
For the ignition
lock cylinder, refer to
How-To: Fixing a Sloppy GM Tilt Column and disassemble just to the point of replacing the lock cylinder.
For the ignition
switch, remove the A/C duct crossing under the steering column and then the small lower dash plate directly below the column. The ignition switch is inaccessible without dropping the steering column. Set the ignition key in the OFF position and adjust the tilt column to neutral tilt, so the steering column is straight. Remove the two 15mm hex nuts that retain the column in place and lower the column to rest on the seat. Unplug the two ignition switch wiring harness connectors; the connectors are keyed and must be removed in a specific order. Contort to remove the two (5.5mm or 7mm hex) ignition switch retaining screws and lift the ignition switch vertically off the column to disengage it from its actuator rod. Be careful that you don't lose the two small retaining screws.
The new switch should be set to OFF by default. Settle the switch down onto the rod to engage the rod socket and reinstall the switch retaining screws. Reinstall the harness connectors in reverse order. Before assembling any further, check to verify that the ignition switch is properly adjusted for correct ACC-LOCK/OFF-RUN-CRANK detent and operation with the column tilted to both extremes. Note that the switch will be easiest to rotate in the neutral tilt position. Loosen the switch retaining screws enough to slide the switch up or down the column to make an adjustment if necessary. Once you are satisfied with the switch adjustment, raise the column and reassemble in reverse order. Torque the column retaining nuts to about 27 ft-lbs.