Turn off the drill and unplug it or remove the battery
Hold the drill firmly
Locate the chuck at the front of the drill
Open the chuck by turning it counterclockwise or using the chuck key if required
Remove the old drill bit
Insert the new drill bit straight into the chuck
Tighten the chuck by turning it clockwise or using the chuck key
Make sure the bit is centered and secure
Reconnect the power or reinstall the battery
Test the drill briefly before use