While the terms are often used interchangeably today, there is a distinction. Witches practice magic and sorcery (spells), and may or may not follow a religion of any kind. Wiccans are followers of a particular Nature religion.
The original Wicca involved both Nature religion and spell-working, but present-day Wiccans may follow just the religious aspects.
In other words, you can be a witch, or a Wiccan, or both.