subfolder install for twentythirteen

I installed WP in a subfolder and am using twenty thirteen theme. Has the index.php file changed from twenty twelve theme? I went to change the index.php file to require (‘./subfolderName/wp-blog-header.php’); [this is what I did with a twenty twelve theme ] but cannot find that code. I wanted to move the index.php to the root folder but now I am unsure how to create that redirection to the subfolder. Thanks for any help as I am fairly new to this.
WD