You'll have to update your core first.
Is that mandatory?
I had an "older" agent working with a new core (for a day before I upgraded them) however I do not think it is recommended.
I mean, why keep the old one? however since you may go to the process of updating, why not test the newer implementation? 2017.3?
Do a side by side migration, test and deploy as you go.
In case you still want to go the 9.6 route: Best Known Methods for Installing LANDESK Management Suite 9.6 (with videos)
Thank you for your advice.
Let's suppose that I can't update the Core however I must to update only the Agents. Is that viable?
I can't tell, someone else will have to pitch in.