We strongly recommend that you use FileZilla. Not only because it's open source, but because it's one of the best FTP applications online. Find more information about FileZilla below:

Supported OS: Windows, Linux, and OS X
Download (free): http://filezilla-project.org/download.php?type=client

How to install the application can be found below:

Windows: http://wiki.filezilla-project.org/Client_Installation#Installing_on_Windows
OS X: http://wiki.filezilla-project.org/Client_Installation#Installing_on_Mac_OS_X

If you are not familiar on how to use FileZilla, no problem. Below is a link that will give you everything you need to know about FileZilla (and a lot more). The resource is: http://wiki.filezilla-project.org/Using