How do I get a Save File:
You can`t copy the save on the normal way, so you have to use a Homebrew Application
Use the Savegame Manager GX to get your save

Uploading Your Save File:
When you upload your save file, all your ghosts will be added to the database.
This includes any ghosts that you have downloaded, such as WR ghosts.
The ghosts on your file will be checked for rapid fire and will be available for anyone to download.

How to use RKG Files:

Method 1: Riivolution
Place the downloaded .rkg file(s) in the Mario Kart Wii folder that you use for Riivolution.
The expert ghost on that track will be replaced by the ghost you downloaded.
This means you must have the expert ghost unlocked in order to view the ghost.

Method 2: WiiScrubber
Replace the corresponding .rkg file in Filesystem/Race/TimeAttack/ghost2 with the ghost you downloaded.
You must have the expert ghost unlocked to view the ghost.