Unfortunately, it isn't possible to 'undo' an upload.
If you wish to remove test sheets that were uploaded to the assessment, you can do so by 'deleting' them.
1. Click 'View Results' on the course dashboard.
2. Go to the 'Responses' tab.
3. Select the specific responses that you would like to delete. The 'Delete' button will display the number of students that are selected.
If you wish to delete all the responses, click the checkbox in the table header.
4. Click the 'Delete' button.
5. To confirm the deletion, click 'Delete' on the pop-up window.
6. Re-upload the test sheets to the desired assessment.