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Cleaning your windows 7 registry requires specialist software. It’s not possible to use regedit to manually edit the registry. Removing the corrupt and unnecessary keys by hand can be very complicated and time consuming. It’s also very likely that your computer will be worse off by trying to manually edit the registry. check the link below..

Windows Registry is a collection of records of all system settings, hardware settings and software settings. It is a part of Windows operating systems such as Windows XP, Windows Vista, Windows 9x, Windows CE, Windows NT, Windows 2000 and Windows Millennium.Computer’s performance can be affected badly with a single deleted or modified registry entry. It is the reason why the most majority of malwares make some changes on the Windows Registry.there are some steps through which you can delete all the unwanted registry file follow the link given below

Try Registry Clean which is designed to safely cleanup Windows registries with only 2 clicks: http://www.acebyte.com/registry-clean.html

With Windex. No, just kidding, but the person who said you can't do it manually is wrong. I do it all the time. You CAN use a program, and it's quicker, like using Advanced System Care, but let's say you install Winamp, don't like it, then remove it. You can go to regedit and search for all instances of winamp and delete them one by one.