First run Dism /Get-WimInfo /WimFile:DVDDRIVELETTER:\sources\install.wim
to see which index the Edition has you want to have alone:
Deployment Image Servicing and Management tool Version: 6.3.9600.17029
Details for image : E:\sources\install.wim
Index : 1 Name : Windows 7 HOMEBASIC Description : Windows 7 HOMEBASIC Size : 11.623.452.494 bytes
Index : 2 Name : Windows 7 HOMEPREMIUM Description : Windows 7 HOMEPREMIUM Size : 12.136.659.100 bytes
Index : 3 Name : Windows 7 PROFESSIONAL Description : Windows 7 PROFESSIONAL Size : 12.037.929.390 bytes
Index : 4 Name : Windows 7 ULTIMATE Description : Windows 7 ULTIMATE Size : 12.200.638.813 bytes
The operation completed successfully.
You want ultimate so run this command with the index 4 for Ultimate:
Dism /Export-Image /SourceImageFile:DVDDRIVELETTER:\sources\install.wim /SourceIndex:4 /DestinationImageFile:C:\Win7Ultimate\sources\install.wim /DestinationName:"Windows 7 Ultimate"
This new ISO should now only include the Ultimate Edition.