The current workflow cannot be altered; but you can create a new work item type your own process and you can customize it accordingly 

 

Where: in Organization setting

 

Restriction: after doing the customization, if you want to use it, you have to create a new project altogether.

 

How:
Go to Organization Settings
Click on the "process" button. Currently, it is possible to develop a personalized procedure by inheriting an existing template.

 

 

Create new Process

• See list of existing process template here, use either of this existing template
  • 
•  
• Give Name and click create
  • 

 

 

Customize Newly Created Process

• Add a new field in user story stage. 
  • Now click and Agile Process, and customize this process accordingly 
  • click on user story, add new field in planning section
    • 
  •  
• Custom Layout  (Using Layout Tab)
  • you can add a new description box.
  • can add new page added altogether.
  • can add new states added.
  • can add new rules added.
  • So basically you can do whatever you want.

 

 

Add New Work Item Type (in newly created process)

• Go to Organization Settings
• Click on the "process" button > Click new added Process ‘Agile Process’
• Click “New Work Item Type”
  • 
• In Next pop up window Add new fields in this newly added work item type
  • 

 

You have to create new project, to use this newly Created Process.