Theres a metal circlip round the plug, use a small screwdriver to push out each end then pull the connector away.
I cleaned mine (when I had one) with autosol metal polish, came up a treat... a dishcloth and some water would be fine i'm sure just dont get any water inside or on the plug...
I cleaned mine (when I had one) with autosol metal polish, came up a treat... a dishcloth and some water would be fine i'm sure just dont get any water inside or on the plug...