Changing wp-config settings

I noticed in the wp-config file for one of my sites that the username was/is for a tech from the web hosting company (I had probably provided access at some stage when the site crashed) and the password was/is one of those ridiculously easy ones – no, not “password” but numbers in sequence>

I’m concerned because I had a problem with accessing the admin section of the site and found a stray line of code at the top of the wp-config file, matching the error message I was getting in lieu of access. So I’m wondering if the file is very hackable and has been hacked.

The DB section reads (with some substitutions by me to explain what is there):

define(‘DB_NAME’, ‘correct name’); // The name of the database
define(‘DB_USER’, ‘webhost tech username’); // Your MySQL username
define(‘DB_PASSWORD’, ‘numbers’); // …and password
define(‘DB_HOST’, ‘localhost’); // 99% chance you won’t need to change this value
define(‘DB_CHARSET’, ‘utf8’);
define(‘DB_COLLATE’, ”);

I want to delete the web host tech user from the database and would like to have my own username and password there but don’t want to wreck access to the site by doing that.

Is there a simple solution to this, please

Site is http://deswalsh.com