At the moment, it isn't possible to change all the question weights at once.
That being said, it is possible to mimic this using the 'Mark out of:' option when exporting the grades to your LMS.
1. From the 'Results Analysis' page, click the 'Send Grades to LMS' button.
2. Create a new grade item in your LMS grade book or select an existing grade item,
3. And Input the desired denominator of the results in the 'Mark out of:' text box. This will allow you to scale the the results to that denominator- effectively, scaling each test question's weight.
For example, if your test has 50 questions, setting the 'Mark out of 100' would make each question worth 2 marks.
4. Click 'Export'