@colin Hi colin
You need to make a new folder for the prerelease. I usually name it whatever the number of the release is. Then when you're installing it and it prompts you to either uninstall or install to a different folder type in your new folder with all the correct / and stuff and continue following the prompts to fire it up.
For some reason I always had to reopen the new folder and fire it up a second time to get the little army guy to show up. probably me just doing something wrong