For one thing, that would break any [~xx~] links you have.
If it’s a test installation, and you are willing to empty out the table, you can trucate the table then set its auto_increment value (at the bottom of the "operations" tab in phpmyadmin) to 1. Then it will start all over.
The sql for that is
ALTER TABLE table_name SET auto_increment=1
I’m not positive, but I think that TRUNCATE table_name will automatically set the auto-increment back to 1.