To completely remove realMyst: Masterpiece Edition from your system, you will need to manually delete the Cyan Worlds folder that contains the Save Game files and Config files. The Cyan Worlds folder on your system is located:
Mac:
UsersLibraryCachesCyan Worlds
*Note, your user's Library folder is hidden by default. To quickly access this folder, in Finder, press the Command, Shift, and G keys at the same time and in the text box that follows, type: ~LibraryCachesCyan Worlds
Windows 7 & Windows 8:
C:Users<User Name>AppDataLocallowCyan Worlds
Windows XP:
C:Documents and Settings<User Name>Local SettingsApplication DataCyan Worlds