A registry on your PC is a part of the software that stores preferences and information about software it has used before. The registry can become cluttered or corrupted, causing your computer to slow down. There are several ways to clean out your registry.

Manual Clean

Manual-clean the registry to have the greatest control over what you erase. To manually clean the Windows registry, you must open the Windows Registry Editor. Open the editor by going to "Start" on your computer and click on "Run." Type "RegEdit" in the Run window and click on "OK." This will open your registry. Click on the "File" section on the top menu, then select "Export" and "Save." This will give you a backup of your registry before you start cleaning out problematic files. To edit files in the registry, click the file you wish to erase and delete the file.

Software

Manually cleaning the registry can be dangerous for the information and software on your computer. An alternative to manually cleaning the registry is to use a registry cleaner software. Many of these, such as CC Cleaner and EasyCleaner, are free to download and easy to use. The interface of these softwares allows you to scan your computer registry automatically. The software will find any files that are damaged or unneeded and clean them from the computer.

Warnings

Cleaning the registry is a task that may affect the way your computer runs. It is important to make a copy of the registry before manually cleaning it and to have a full backup of the data on your computer. Sometimes cleaning the registry can cause catastrophic failure of software, including the operating system. Ensure you have all the install disks for your computer before cleaning the registry.

Source:

One Cleaner

PC World: How Best Do I Clean my Registry

Top Bits: How to Clean the Registry