You can either prune by date or by file. For simplicity, I pruned by file. I connected to mysql and ran the following command:

PURGE BINARY LOGS TO 'mysqld-bin.000044';

But you could prune by date:

PURGE BINARY LOGS BEFORE '2013-08-24 00:06:00';

To update the root user mysqladmin -u root -p'oldpassword' password newpass

To update a normal user mysqladmin -u username -p'old-password' password new-password