Which of the following is the correct syntax for reassigning (updating) the value of the variable winner?

The correct syntax for reassigning the value of the variable winner is simply to use the variable name followed by the assignment operator = and the new value. In this case, writing winner = "Bill!"; effectively updates the value of the variable winner to the new string "Bill!".

This syntax follows the standard practice in many programming languages, where an existing variable can be assigned a new value without needing to declare its type again. Such an operation allows developers to change the content of a variable dynamically as the program runs.

The other options provided do not represent valid syntax for reassigning a variable in languages such as JavaScript or Python. For instance, declaring the variable again (as seen in the first option) initializes a new variable instead of updating an existing one. Using := typically indicates a different kind of assignment used in other languages that are not applicable here. The phrase ‘update winner’ does not conform to any standard syntax for assignment in popular programming languages. Thus, only winner = "Bill!"; correctly updates the variable.