Answer:
It would double in size
Explanation:
Judging as the circumference of a circle is dependent on the diameter, a circle whose diameter doubled in size would double.
An example would be a circle with the circumference of 20. It's radius would be 10 rather than 5. The circumference of the circle with a diameter of 10 would be roughly 31, while the circle with a diameter of 20 would have a circumference of roughly 62.