Thank you for the screenshot you've provided, talk2khurram.
There are two Units of Measure modes in QuickBooks; Single U/M Per Item and Multiple U/M Per Item. The way to change a Unit of Measure depends on which of these modes is currently selected. Here's how:
Go to the Edit menu, then Preferences.
Select Items & Inventory, then go to the Company Preferences tab.
Check the Unit of Measure section.
If you see the Enable button instead of Single U/M Per Item or Multiple U/M Per Item, the Unit of Measure is currently turned off. Select Enable to turn on, then select a mode.