There is a way to upgrade Windows 7 professional to Windows 7 Enterprise that is not officially supported from Microsoft.
here are steps that you should take:
1. Create a .reg file and double click on that with following text.
Windows Registry Editor Version 5.00
[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion]
"EditionID"="Enterprise"
"ProductName"="Windows 7 Enterprise"
2. Insert 7 Enterprise DVD and launch it upgrade option.
[original article http://richardfleming.me/upgrade-windows-7-professional-to-enterprise/]