Below are the functions that let you work with multiple version of a model. Use the list_versions() method to view all available version of a model: 
model_name.list_versions()
Use the get_version() method to use a specific version of a model: 
model_name.get_version(9)
Use the set_active() method to set a specific version of a model as active: 
model_name.set_active(9)
Use the drop_model_version() method to remove a specific version of a model: 
project.drop_model_version('my_model', 3)
Please note that the model version should be deactivated before it is removed.