We present a novel task of playing level conversion: generating a music arrangement in a target difficulty level, given another arrangement of the same musical piece in a different level. For this task, we create a parallel dataset of piano arrangements in two strictly well-defined playing levels, annotated at individual phrase resolution, taken from the song catalog of a piano learning app.In a series of experiments, we train models that successfully modify the playing level while preserving the musical 'essence'. We further show, via an ablation study, the contributions of specific data representation and augmentation techniques to the model's performance.In order to evaluate the performance of our models, we conduct a human evaluation study with expert musicians. The evaluation shows that our best model creates arrangements that are almost as good as ground truth examples. Additionally, we propose MuTE, an automated evaluation metric for music translation tasks, and show that it correlates with human ratings.