how to backup on a hhd, without having to select the files manually

Hi,
I am running a backup hhd with a folder of approx. 1000 files and documents. On my computer I have the exact same folder with documents, which i edit often. The thing is that the backup is a few weeks old. When i use it to backup all my files, how can I copy the content of my computer on to the harddrive withhout having to pick which files need to be copied. Can i mark all the files and copy them, withhout having to deselect all the ones that havent been changed?

If i select all and say copy, Windows comes up saying: This file already exist do you want to replace it. That is time consuming to do 1000+ times.

So is it possibly that Windows or some program finds out by itself which additional files have been placed in the folder on the computer and needs to be backedup, without having to interfer myself?

thanks in advance.