Can I upgrade the created on field?

Can I upgrade the created on field?

Can't seem to figure this out in any area, so I made custom ones for when I migrated my data from Dynamics CRM.  It's just sort of a pain since it shows created on is today for all my accounts, opportunities etc.  I can just look at the custom field I made to see when it was made but it would be nice if it showed the proper date.  I tried editing it which it doesn't let me, and I tried to change it in sheet view but it doesn't save, is it not possible?  What do people do when importing data from another CRM?