If you want to remove the data, you will have to open a shell and delete it.
Assuming mongo
is on the path (and the mongo daemon is running), try this on your shell:
$ mongo //This will start a mongo shell
> show dbs; //This will list all the existing dbs
After you found the name of the db you want to delete, Ctrl+D
to leave the mongo shell, and type:
$ mongo <dbname> --eval "db.dropDatabase()"
Dropping the database will completely remove any trace of data from your system. If, on the other hand, you just want to empty the tables (and keep the dbs), then, after finding the name of your db, type in the mongo shell:
> show tables;
> db.table_name.remove();