How can I change the Project number for a project just created?

Summary

How can I change the Project number for a project just created?

Content

I Just copied a project from another project and changed the project number to a wrong number. It got created as an approved project and I changed the status to 'Draft'. I am trying to click on edit for basic information to change the project number to a correct number but it doesn't do anything though it allows me to edit other sections. 

Is there any configuration that is preventing me from doing? How can I change the Project Number?

 

Regards,