1) Please download the free Notepad++ for whichever home computer you are using (pc,mac,linux) http://notepad-plus-plus.org/download/ (Please use the big green button if you have windows, otherwise look below for mac or linux). Install Notepad++ with default settings.
MAC USERS - Please read this to learn how to get Notepad++ working on your system http://studiogreenleaf.wordpress.com/2012/05/10/notepad-on-mac-osx/
2) Unzip the theme file that you've downloaded from themeforrest.net and inside you will find a second zip file (This was the theme zip file that you've uploaded to your host before in Wordpress Admin.) . Unzip this second file on your desktop (or wherever you keep things on your home pc).
3) Open Notepad++ and hit Ctrl F (the controll button and the letter F) which should open up the Find box. Take a look at the image below and use it to define the folder where you unzipped the theme in step 2 above , and enter the keywords you are looking for and you will instantly be shown the line number and the name/location of the file(s) that contain those keywords
The letter D below is where you would put the keyword you are looking for and remember that capitalization counts.
This is what I use to find things, its quite handy.