What should one who has embraced Islam do with a golden cross they possess?

Your friend is not permitted to benefit from the cross by selling it or gifting it as long as it retains its form. He must remove its form by melting it or breaking it, after which he has the choice to sell it or gift it. This is based on the Prophet's (peace be upon him) saying: "He would not leave anything in his house that had crosses upon it without demolishing it."