It is a dummy question, but, I'm being trying to change the /etc/yum.conf but the file appers to be "locked".

Thu Mar 14 08:06:59 root@pxl1pscnd037:/etc [0] # ls -sla yum.conf
4 -rw-r--r-- 1 root root 675 Dec 14 14:06 yum.conf
Thu Mar 14 08:07:07 root@pxl1pscnd037:/etc [0] # getfacl yum.conf

file: yum.conf

owner: root

group: root

user::rw-
group::r--
other::r--

Thu Mar 14 08:07:12 root@pxl1pscnd037:/etc [0] # rm yum.conf
rm: remove regular file ‘yum.conf’? y
rm: cannot remove ‘yum.conf’: Operation not permitted
Thu Mar 14 08:07:17 root@pxl1pscnd037:/etc [1] #

What can I check to make yum.conf writable again?
Thanks,
Igor Bajo.