Our system standard field cannot be changed by default, unless you have created a custom field, then this field can be changed by the user if they have permission to do so. Custom Field is created at the Core module under Setup, Custom Field Setup. You may check your user's permission as follows
Go to EPE Control and click Security Setup
Log in and select User Settings.
Select your user and check the Security Group
Click on the Security Group tab and select the Security Group ID to verify the permission