Hi Vishal ,

You can change the UOM of the products as follows.

Go to Sales -> Configuration - > Settings -> in unit of measure select some products is sold/purchased in different in UOM.

Then come back to product form , then you can see the fields to set the UOM for the products.

To save a uom as default, just activate the developer mode , then select the required uom in the field, then open the developer tools. select the set as default option, then just save the uom from it.

Thank You

Niyas, Thanks for responding to my question. I can see the UOM data on the Product page, but what I would like to change is the "weight" of the product in the "DELIVERY NOTE". 

Sales Order --> Delivery --> Additional Info --> Weight. This is set to kgs. How do I make this in lbs. I have changed the defauls unit for Weight to lbs from kgs.