You need a real copy of the game. SD card, HBC on your Wii, and the apps save extractor, and installer.
From there with the game in your Wii. Use the extractor and remove the file. If will be in a folder on your SD. Next use the tools on this site ACToolKit to open the game's master file. Which is called RVFOREST. Make a copy of that file to be safe. From There use the software and edit your town. Check out Youtube for videos on how to use it.