I think that you should have gone to the Contribute forum, but seeing that you have landed here, we may be able to help.
To answer the question, have a look here Connecting via FTP to Your Site Using Adobe Contribute or Google the subject.
I now you didn't ask but you should know, you really need to look for a different way to create and edit websites. It's only a matter of time before Contribute will be worthless. Best to plan for something else before that time suddenly gets here.