Remove the Reaktor 4 installation by dragging the application to the trash. You can also trash the preferences from the Library>Preferences folder. They are called Reaktor4.plist and com.reaktor4.plist respectively. If the program refuses to delete from trash, it may be locked. Take the icon out of the trash and put it on the desktop. Highlight the icon by clicking on it once. Then type apple-I. You should see a box that says "locked". If this is checked, uncheck it and try to delete the application. Alternatively, you can hold down the option (apple) key while choosing "empty trash" from the finder. This will force delete any locked items in the trash. A second possibility is to use a third party application to delete locked items from within the terminal application. A good free program is called "Cocktail" it has many functions, one of them being to force empty the trash.