the way Lightbeamer showed is indeed a possible way to replace existing Devices with new versions or other Devices. However, in large projects, this method takes its time.
Today, there is no direct function to replace a DDf in the project itself via DMXControl 3. However, you can open the project file with your normal file browser (the project-file is a normal zip-file) and replace the existing DDF in the project with the new DDF. As Lightbeamer said, make a copy of your project before you change it.