In view of my prior frustrating experience upgrading a Microsoft product (complete reinstall), I was pleasantly surprised when I found out how you upgrade a SharePoint install from the Standard edition to Enterprise: just change the license key!!! Wonderful, I look forward to seeing this kind of simplicity when upgrading their other products!
Change the License Type
Go to Central Administration à Operations. Select Convert license type.
Enter the license key for the Enterprise Edition
Enable Enterprise Features
Go to Central Administration à Operations à Enable Enterprise Features
Choose Enterprise and click Ok.
Enable Enterprise Features (Existing Sites)
Go to Central Administration à Operations à Enable Enterprise Features on Existing Sites
Check the box and click Ok.
(Once you upgrade, you can’t downgrade to Standard again)