You can use the same syntax you would to access the folder when you're on the command line. the following will all work:
"../../file.txt"
"relative/folder/file.txt"
"/absolute/folder/path/file.txt"
This is the syntax in *nix, but it sould work exactly the same in windows. "If you think you're too small to make a difference, try spending a night in a closed tent with a mosquito."