when you install downloads, they are essentially put in a seperate folder. To remove the download, you just have to go to folder you put in it initially(I think it's "updates" or "dlupdates" or something like that. The readme that comes with the download should say the folder it goes in) and take out the files for the download (usually just one, but for some things it's two files). You can either delete the files entirely (by clicking on the file and pressing the "delete" key on your keyboard) or you can take the file out and save it somewhere else for safe keeping. I myself have a folder in My Documents labeled "ZooTycoonQuarantine" for downloads that are causing me trouble or I just don't want in my game but don't want to completly delete. I recommend setting up such a folder (name it whatever oyu want) to store downloads in case you want them later.