Instructions
Insert Mario Kart Wii into your Nintendo Wii and power the system on. From the main menu, navigate to the Time Trial mode.
Select a track and choose to race against the staff ghost. Beat the staff ghost by between three and 10 seconds. The specific time depends on the course. For example, while the Flower Cup course, Mario Circuit, only requires you to beat the ghost staff by four seconds, the Leaf Cup's DK Jungle Parkway requires you to beat the staff ghost by nine seconds. After beating the staff ghost for a given track, you'll be able to race against the expert staff ghost for that track.
Repeat Step 2 for all of Mario Kart Wii's 32 tracks. You'll know you've beaten the normal staff ghost for a track when a faster ghost with a shorter time takes its place.