change database user

How do I change the database user for my database? Do I just do it in the config.php file or is this too simple. My server told me to change the user name because I have the same username for several databases and I sometimes exceed the number of max user connections. I have been running wordpress for several years and last night all my database sites (including phpBB3) crashed.

Any help would be appreciated.

Here is what the server techs said:

Looks like your script uses PConnect function to connect to our sql server. He have to use mysql_connect function instead of pconnect. Please recheck all your scripts and change the PConnect(); function to mysql_connect (); function.
Your websites are working now, but you need to optimize your databases and scripts. I found that you have used only one sql user to connect to all your databases, but the max_user_connections for the user = 50 connections. You have to add additional users for all your databases.(Go to Mysql from your control panel) then you will need to reconfigure all your scripts, set a new sql user for them instead of “h0lapv_rick”