Air Explorer allows to work between two or more FTP accounts.

First, add your FTP accounts.

Once you have added the FTP accounts, you can open one FTP account in one side, and open in the other side the other FTP account.

You can paste, copy, drag&drop, between the two windows with FTP accounts.

You can check more information here:
-WebDav in Air Explorer
-FTP and SFTP in Air Explorer
-SFTP in Air Explorer
-FTP transfer with Air Explorer