Final answer:
A change in accounting principle should be accounted for retrospectively, where financial statements are adjusted as if the new principle had always been used.
Step-by-step explanation:
The correct answer to the question 'A change in accounting principle should be accounted for how?' is c) retrospectively. When a change in accounting principle is made, it is applied retrospectively to all prior periods presented in the financial statements, unless it is impracticable to do so. This means the financial statements are adjusted as if the new accounting principle had always been used. The alternative, accounting for changes prospectively, involves applying the new principle to transactions, other events, and conditions occurring after the date that the principle is adopted.