The documentation (in the Gamer's Guide) says you should be able to preview it using an "Enter Player Mode" button next to "Begin Game Session" at the end of the Home Ribbon, but I don't have that button.
To change users, use a different Windows user account or go into your User folder and move, rename, or delete the Realm Works local database folder at:
Code:
explorer "%APPDATA%\LWD Technology, Inc\Realm Works"