You can change order status by:
1. choose the order
2. select item(s)
3. choose the next status (for example 'Ready to Pack')
4. on the confirmation screen, click 'Submit'
In case there is more than one 'next status', you can click to downward arrow next to the status button. Option(s) defined in the workflow will be shown.
In above example, other than 'Ready to Pack', the alternative option defined in the workflow is 'Cancelled'.