Click here to goto CCleaner website. To clean up your Registry run CCleaner. Click the Registry button, then the Scan for Issues button.
When you click the button labeled Fix selected issues the program will ask if you want to save a backup of your registry. Answer yes.
If something goes wrong you can restore the registry from this file. I've never needed it.
Finally you may have to click Fix All Selected Issues. Your computer should run faster and have fewer problems if do this every 3 to 6 months.