Changes the order an entity's tabs appear in — site-wide, for every user, not a personal preference. Applies to any of the 11 entities that have their own tab set.
Side menu → Site Admin → Site Settings → the Tab Order tab.
Choose which entity's tabs you want to reorder from the dropdown:
The list shows that entity's tabs in their current order. Drag an item to a new position, or select one and use the Move Up / Move Down toolbar buttons.
Click Save. The new order applies immediately, site-wide, for every user — this isn't a personal/per-user setting.