You cannot remove a question if there are active attempts. However, you can change the score for the question to "throw out the question" and prevent students from being penalized. To achieve this, you may follow the steps below:

"Throw Out" a Question on an Attempted Assignment

1. Go to the course and navigate to the assignment.
2. Click Edit for the assignment and select Edit Questions.
   
3. Click in the points field for the question to be be "thrown out" and enter 0.
   Note that the overall assignment value has decreased by the number of points that were removed.
    
4. To keep students from being penalized, you will need to manually reallocate the removed points (10 in our example) to one or more of the remaining questions following the procedure in Step 3 above.
   
5. Save & Exit.