Final answer:
To convert a CSV file to an XLSX file, open the file in a spreadsheet application, then use the 'Save As' function, choose 'XLSX' format, and confirm the conversion by clicking the 'Convert' button.
Step-by-step explanation:
To save a CSV file as an XLSX file, you'll need to convert it. To begin, open the CSV file in a spreadsheet program like Microsoft Excel. After you open the file, initiate the conversion process. Typically, you'd find an option to 'Save As' in the File menu. Choose this and then select the 'XLSX' format as your desired file type. You may be prompted to confirm your choice, so look for the Convert button in the dialogue box that appears. Clicking 'Convert' will finalize the conversion from CSV to XLSX. Remember to choose a location on your computer where you want to save the new XLSX file.