Generally you should first update Seblod. but if you are on very old Joomla version you will need to do it in few steps as sometimes new Seblod version requires new Joomla, e.g. this was the case when Joomla changed its databases encoding (I believe in 3.8). Joomla and Seblod versions always go in parallel. The best is to read release announcements and change-logs and update regularly.