Runtime content editor is a special executable file named DISEditor.exe that is included automatically with each project in its folder. The purpose of DISEditor is to allow you to update the project's content in a simple way directly on the computer that runs the project without going back to the project designer program and transferring the updated project again.
To start the editor simply double click on the DISEditor.exe file in the project's folder or press F2 while the project is running. Please note that if you started the project through the Preview project option in the project designer program then pressing F2 will not have any effect. That is because the editor is made only for use at project's runtime and you should not use it while you have the project opened in the project designer program.
When the editor starts it analyzes the project's structure and shows you controls for editing content for each relevant media object starting from the first scene in the project's timeline.