Salesforce Data Loader provides a way to delete a large number of records at a time. If you want to delete a large number of records, follow the steps:

Step 1: As a backup measure, if you are going to delete all the records then sure you have selected all the fields and export the records to delete (for more see Export Data.) and remember to save an extra copy of the generated CSV file.

Step 2: And after, exporting the records you wish to delete, this time using only the record ID as the desired criterion.

Step 3: Now, launch the Data Loader, and use the wizard of delete or hard delete wizard. In the wizard map only the ID column. For more info see Insert, Update, or Delete Data Using Data Loader.

Step 4: At last, after completing the wizard operation, review your success and error log files. See Review Data Loader Output Files.