Centos Linux operating system can be downloaded from Centos Public Mirrors. Most of the download locations are at US. Current version is 6.3 now. DVD version consist of two files. CentOS-6.3-x86_64-bin-DVD1.iso and CentOS-6.3-x86_64-bin-DVD2.iso.
Find and replace feature is always handy. It can turn into a torture when it comes to change or delete a simple constant string in a text file. There is a handy tool in linux for doing these kind of tihngs. Actually sed is not a text editor but it is used outside of the text file to make changes.