Your rosters will automatically roll into the new school year exactly as they are, so there's no need to re-add the same staff.
However, you might have a few new hires incoming, or folks moving on -- we've got you covered!
Three months before the end of your current school year, you will see a banner up top on the Staff Manager:
Clicking the blue Update staff in the next year button will take you into the next year's roster. Here you can add any new hires starting next year, or remove any folk due to leave, all while preserving the integrity of your current year's roster.
Note: Don't forget to click the blue button to return back to the current school year when you're done!