In the Data Sources section, you have all the data sources of your project available. If you want to delete one of them, you must click on the three dots to the right of the data source and select 'delete data source'.

You can also click on each data source and delete it using the ⚙ icon.

Once you delete a Data source, all the data it provides to your audience will be removed and contacts with no other data sources will be removed as well.