What version are you using?

To begin you will need the installation files for the server. These can be downloaded from the Sage website with support, but I am not certain that this can be done without an active support contract. If you have the install files from the most recent install you should be able to install using them as long as the server OS will work with your version. You would then be able to move data files and such to the new server. Any connected applications you may have installed on the Sage server may also require installation and configuration on the server or any client machines you may have.

For specifics more information about the environment would be necessary.

They would need to have a support plan to download the CD image, and generally only the most current versions are available for download, so the version they are running may not even be available to download. If they have a CD still (since I don't know what version they are running) or have saved a copy of the CD image and any updates for that version they are running they could use that. Migration is complicated and there is much to consider. They may need to contact their Business Partner or Sage 300 CRE Sales to arrange to get an image of the Sage 300 CRE CD version that they are running.

My recommendation would be to get a consultant involved to assist with the migration.