3.3.2 is a more recently released modeler version than 4.0.1, you can't convert from 3 to 4 just because the major version is higher. The easiest way is to wait for 4.1 and then convert to that.
Or you could manually edit the modeler database but if you are actually using features that were added to the model in 3.3.2 (and are thus not in 4.0.1) you could corrupt your project.