To change the default font in Excel, follow these steps:

1. Open a new or existing Excel workbook.
2. Click on the ‘Excel’ -> ‘Preferences’ in case of Mac and ‘File’ tab -> ‘Options’ in case of Windows
3. In the ‘General’ tab, scroll down to ‘Default Font’ then Click on the drop-down menu next to ‘Use this font’ and select the font you want to use as the default.
4. Optionally, you can also change the font size and style.
5. Close and restart Excel for this change to be in effect..

From now on, every new workbook you create in Excel will use the font you selected as the default. Keep in mind that changing the default font will not affect any existing workbooks you have already created – you will need to change the font for each of them individually.