As you may know Ndless tightly integrates with the TI-Nspire OS, and each installer is developed for a specific OS version.
The latest Ndless 3.6/3.9 is not compatible with OS 4.0. Do not upgrade to OS 4.0 at the moment as you won’t able to downgrade and use Ndless! If you want to know more about the OS dowgrade protection and the cat and mouse game between Ndless and TI, read this post.
You should know that updating the Ndless installer is hard work. Please subscribe to new posts to be notified once its ready. No ETA can be given, sorry for the annoyance if you were wrongly adviced to update by Student Software (and blame TI for it).