We suggest you archive the leads instead of deleting them because that way you will know if you import those same lead in the future. (archived leads are matched against other leads during duplicate detection).
If you absolutely need to delete leads, the only way you can do so is by moving them to a separate list using a pipeline automation and then deleting that list.
Start by creating a new empty list - use the list where you have the leads you want to delete as a template, to make sure the fields in the new list match those of the old.
Then create a pipeline automation (or a one-off migration if you are not on the Plus or Premium plan).
Pipeline automations (or migrations) will allow you to isolate the leads you want to delete, by filtering them by state, category, claim status, due status or by any data using conditions.
Filter options for pipeline automations
If you can isolate the leads you want to delete, you can move them to a new list, and then delete that list.
If you can't migrate the specific leads you want to delete, then you'll have to run through the list and archive the ones you want to be deleted, and then you can delete them using the method described above. Please note that, when archiving them, you need to do so with a specific category, so you can use this method.
Here is a short video of the process:
If you're interested in updating and not deleting the leads, click here.
To read more about migrations, click here.