To upload a single file to the FTP, or a group of files, this is what you have to do. Go to:
Tools -> Deployment -> Configuration...
Press the plus + to add a new configuration. Give it a name and select its type. Fill then all the info for the connection.
When finished, press the test button to check if the configuration is correct, and then go to the Mappings tab to see if all paths are filled.
You can then select a file in the project browser, and click on it with the secondary button to do:
Deployment -> Upload to <server name>