Updating files

I have a Macbook running osx lion 10.7.5, Lets say I have 2 identical folders named "car", one in "Documents" on my harddrive (HD car) and one on a USB stick (USB car)and I want to back up the car folder from the HD to the USB periodically. When I copy HD car to the USB instead of replacing the files in USB car with the newer files, it tries to copy the entire HD car folder to the USB. however when I select all the files inside HD car and drop them into USB car it asks if I want to keep the newer files. This is what I want. Is there a way to do this by just dropping the entire folder onto the USB. This is a folder I don't want in Dropbox or any other cloud based storage

Thanks!