I have created a part and tried to change the state of it. But I was unable to change it.
Owners of Part items are able to manually promote items to the released state. The other way to manipulate the state of an Item is using a change item. The workflow of a change item like an ECO will promote affected parts to the proper life cycle state. More information on these processes can be found by accessing just ask innovator. Within innovator navigate to help > Just ask Innovator. There is information about life cycles as well as how to manipulate them with workflows.
I guess, the manual promotion is based on the role assigned in Part Life Cycle. By default, it will be ARAS PLM.
To Manually change the state of the Part
You can promote using below AML query (GUID of the Part item)
<Item type="Part" action="PromoteItem" id="57CA6B0F30DC4A48B8F82A111A1CSAC6" version="0">