Enable Registry editor

You don't need to enable registry as it is enable by default.
To open registry follow following procedure:
Start
Run
regedit

If it is disabled by anyone then follow following procedure:

Type the following text in registry and save it as enable.reg.
[.reg is extension for regfiles]

REGEDIT4

[HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Policies\Explorer]
"DisableRegistryTools"=dword:00000000