Log file questions

How can I increase the size of any given log file?
I am running COL 2.3 and Samba as a server. I have no problems logging in. However, the following shows up in my log file:
Jul 23 20:18:15 server PAM_pwdb[883]: 1 authentication failure; (uid=0) -> brianw for samba service

In reality, there is no error. I log in fine and access all of my files. From the workstation standpoint, there is nothing wrong.

Any help would be appreciated.

Brian