xcopy is one of the most powerful dos commands. It is mainly used for copying files, but arguments create a monster of it 
To use xcopy to update a folder from another you need to use :
xcopy H:\somefolder\*.* C:\updating\ /s/d/y/h/r
Here we are updating C:\updating using files in directory H:\somefolder.
Let's see what those arguments mean:
- /s - copy subfolders
- /d - compare files by date (copy newer changed files only)
- /y - yes to overwrite and all the questions pc may ask
- /h - copy hidden files too
- /r - copy readonly files too
More info : xcopy help.
