Upload only changed files

I'm looking for a way to make SmartFTP only upload files that have a more recent timestamp than the ones on the server (ie: files that have changed).

I cannot find this option anywhere in the SmartFTP settings, or any reference to such an option on the website.

Is there an option for this?

If not, why has such an obvious (and I thought standard) feature been missed out of an otherwise very competent FTP package?

I'm actually looking for the reverse of this functionality - want to backup my website down to my PC but only files that have changed. Is this possible?

I guess this isn't possible then? Its a shame, cos I like this software but without this feature I'll have to change to something else