Pls I would like to know how to disable directory listing for my Cent O.S server default i.p like 126.96.36.199
Would like to know which of the conf file that I would edit
Is it this file /etc/httpd/conf.d/welcome.conf that I would edit
No, welcome.conf isn't that. Read about
The 'welcome.conf' file in RHEL derivates is meant as a starting point. You should probably create your own config, more fit for your setup.
Regarding disabling directory index, this is a simple google search away: