Navigate to Tools>Incident>Field Management, and click Edit beside the relevant register. 

Renaming Tabs

1.  To rename a register tab, click the Rename Tabs button: 

2.  A list of the available tabs in the register will appear, and clicking on any of these tab names will allow the existing text to be updated.  Once updated, click the blue tick, then the Save & Close button.  Again, remember to click the green Save Register button (top or bottom right) before leaving the page to ensure the changes take effect.