i will use pal to ntsc for this guides explanation.
1. Make a game save for both regions
2. Download Save Game manager GX if you dont already have it
3. Open Save Game manager GX and extract both the pal and ntsc game saves to either hdd or SD
4. Go to your computer and open the extracted game saves folder for both regions.
5. Delete everything in the ntsc folder except the banner.bin file
6 copy and paste everything from the pal folder except the banner.bin into the ntsc folder
7. Plug your SD or HDD back into your wii and load up save game manager gx
8. Install the new ntsc game save and once that's finished load up the game of the save you just converted and see if it worked.
*Note this night not work for every game and always make sure to have a back up of your original save encase things go wrong*