Hello, how to deupgrade win7 ultimate to win 7 professional
You'll have to format your system to do that. That is, format your current Win7 Ultimate, backup before you do this or keep the older files, so that they'll appear in the 'windows.old' folder, and then install Win7 Professional from your disk.
Windows 7 Ultimate has all of the features of Windows 7 Professional, why do you want to downgrade?
OP might not be having the disk for Ultimate. It may have been pre-installed. He may only be having the Professional disk.
It's perfectly fine to burn a generic Windows 7 CD. There's only one install CD for all editions, they're usually just configured for a specific one to avoid consumer confusion. If the OP has an Ultimate key then he can reinstall it easily.
Only with fresh installation of Win 7 Pro. Back up all critical data and do clean install, windows doesn't have downgrade capability, only upgrade.