Using FTPS in Windows Server 2008

Here's the way that you specify which type of FTP over SSL (FTPS) that you are using in Windows Server 2008:

• If you enable FTPS and you assign the FTP site to the default port of 21, you are using Explicit SSL.
• If you enable FTPS and you assign the FTP site to port 990, you are using Implicit SSL.
• In point of fact, if you enable FTPS and you assign the FTP site to any port other than port 990, you are always using Explicit SSL.

Explicit FTPS versus Implicit FTPS

Configure FTPS Server Using IIS

or search for "set up ftps on iis"