asensei will downloads workouts automatically for you so that they are ready when you come to workout. Media files are pretty big and even though we try and optimise the size of our workouts, over time this will start to occupy a decent chunk of your storage space.
From app version 1.8.0, you can free up storage by deleting workouts that have been downloaded. To do this you have to go to the Workouts list. Hit Hey asensei [+], then Workouts, then choose a program from the list that appears. The workouts that have been downloaded will have a blue bar underneath them. If you swipe left on one of those workouts you will be given the option to Remove download. You will see a warning message pop-up asking if you are sure. Removing the download will only delete the associated video and audio files, not your workout results (if you want to delete those see this article: Can I delete a workout session summary?)
We have plans that will allow for even more control of your storage, but if there is something you'd like to see us do please tell us at firstname.lastname@example.org