I've written a lengthy explanation of how to clean up a messy context menu, using either the registry editor:

If you want to clean things up the truly geeky way, you can open up regedit.exe through the start menu search or run box, and then browse down to one of the following keys…

Most of the menu items that used for all files and folders can be found by looking at one of these keys:

HKEY_CLASSES_ROOT\*\shell

HKEY_CLASSES_ROOT\*\shellex\ContextMenuHandlers

HKEY_CLASSES_ROOT\AllFileSystemObjects\ShellEx

Items that are specific to folders can usually be found in one of these keys instead:

HKEY_CLASSES_ROOT\Directory\shell

HKEY_CLASSES_ROOT\Directory\shellex\ContextMenuHandlers

You can read more at: How to Clean Up Your Messy Windows Context Menu

Or use some freeware NirSoft tools like ShellMenuView or ShellExView.