The best way to make changes to a default template in Joomla would be to use the template override feature. This allows you to create copies of the default template's files and make changes to them without affecting the original files.

Here are the steps to use the template override feature:

1. In the Joomla administrator interface, go to Extensions > Templates > Templates.
2. Find the default template you wish to modify and click on it.
3. In the left sidebar, navigate to the "Overview" tab and click on the "Create Overrides" button.
4. Select the files you wish to override, such as the layout or module file.
5. Once selected, Joomla will create a copy of the selected files in your template's "html" folder. These copies will now be used instead of the original files.
6. You can now make any desired changes to the copied files and they will be reflected on your website.

It's also important to mention that you should always make a backup of your template before making any changes and also to ensure that your template is compatible with the version of Joomla you are using and also in case of future updates.