How to burn an ISO file larger 4.7 GB onto a DVD

It's just a matter of media.

If the DVD ISO you have to write onto the media is bigger than 4.7 GB, you can use double-layer DVD if your writer is able to support this kind of DVD.

Then you can put almost the double of 4.7 GB on a single double-layer DVD. Of course, if the ISO size exceeds the size limit of a double-layer DVD, you cannot do anything more with a DVD.

There are two links to download CentOS 7 (the latest version) from the download site at centos.org. If you choose the first link by clicking the button that says DVD ISO you be asked to select a mirror and then download a 3.9GB CentOS ISO file that will fit nicely on a DVD. Clicking the other download button will download a bigger ISO that has a lot of additional packages that you don't need.

Alternatively CentOS can also be written to an 8GB USB flash drive (or larger than 8GB) using UNetbootin from the default Ubuntu repositories. For general instructions about how to create a bootable USB stick using UNetbootin see this answer.

UNetbootin has been dropped from the Ubuntu 18.04 repositories. When I tested the built-in Startup Disk Creator application as a UNetbootin replacement app with 3 non-*buntu live .iso images it worked in Ubuntu 18.04.