Generally, a revert can keep their existing family surname, such as Joseph or Sharma, after converting to Islam, since surnames typically function as lineage or family identifiers rather than statements of religious belief. Many reverts choose to keep their family surname unchanged, both as a practical matter (maintaining continuity on official documents and with extended family) and out of respect for their family heritage, while adopting a new Islamic first name that reflects their faith. The exception would be if the surname itself has a direct shirk-based or clearly religious meaning tied to another faith’s worship (which is uncommon for most surnames) — in such specific cases, individual guidance from a knowledgeable scholar is advisable.