If you are using OpenVZ virtualization, we now have CentOS 7 images available for download. Just login to Cloudmin and go to Cloudmin Settings -> New System Images, search for CentOS 7 and download the ones that you want. We have an image with just the base OS, and another that includes Webmin and Virtualmin GPL.
Please note that a 64-bit host system is needed to run these images, as CentOS no longer supports 32-bit installs.