For the question you want to remove, select Delete question (trash can icon). Your question, all of its translated versions, and any response data you've collected for that question will be permanently deleted.
Note: If you create your form in Excel for the web or create your form in OneDrive for work or school, and then delete a question, the question and all of its translated versions will be permanently deleted. If your form and Excel workbook data are in sync, however, any previously collected response data for that question will remain in the workbook.