how to change sybase sql default port
Sybase ASE retrieves port numbers for the listeners from the interfaces file. On *nix systems, this is typically in the Sybase Home directory ($SYBASE/interfaces)

On Windows systems it's called interfaces.ini and can be found in %SYBASE%, which is likely to be c:\sybase (I think..been a while since I've run on Windows).

I believe you can launch the GUI interfaces editor through Sybase Central, if you are using that to manage your ASE databases.  dsedit and dscp are the two utilities that can be used to edit the interfaces file.  

You can also manually edit the interfaces file using a text editor such as vi but be sure to pay attention to the format of the entries and permissions, so as not to accidentally muck it up.