From The Document Foundation Wiki
How to change the order of individual sheets in the spreadsheet
Follow these steps :
- Select the sheet which you want to move.
- With the mouse positioned on the tab of the sheet, right-click to access the contextual menu and choose Move/Copy Sheet.
- In the dialog that appears, make sure that the Copy option at the bottom of the dialog is not checked.
- In the list Insert before, select the desired position.
- Click OK.
Another technique is to click on the tab and drag it to the desired position among the other tabs.