Navigate to the Organisation and Users via the Menu.
Click on the + icon next to your Organisation to show the Organisation Units.
If you have Units nested within Units, you may need to click on the + icon again to find the Unit you want to amend.
Click on the Unit's name.
Click on the Details tab on the left-hand side.
Rename the Unit in the Name field.
Click Save. The new Unit name will now be applied.