I'm using solid Edge. why should i cant download step or IGES file??
You will only be able to download files in formats that were uploaded. If all that was uploaded were say SolidWorks files you will not be able to get them in another format. Try asking the designer to upload the generic format you need. Most are willing to help.
Solid Edge can easy import a very big range of file formats, I am sure that you can download one of those.