You'll have to find all DEFINES for this description - use the Developers Tool Kit in ADMIN->TOOLS to search for files with these defines. Use the input field right at the bottom-left and type in any text you'd like to find appearing in the php files. Select "All Files - Catalogue" in the dropdown that appears to the right of this input field. (You probably won't need to change defines in ADMIN as your shoppers don't see this side of the shop).
The system will search through all 950+ php files, then LIST all those where your text string appears.
PRINT OUT THIS LIST.
Be aware that making these changes MIGHT upset other functionality. Don't change items that relate to database tables or other functions.
The text you are looking for is likely to appear in lines that look something like this:-
define('HEADER_TITLE_CART_CONTENTS', 'Shopping Cart');
BE CAREFUL to alter the text ONLY between the second pair of single quote marks:
define('HEADER_TITLE_CART_CONTENTS', 'Booking Cart');
DO NOT remove the single quote marks... And if you put text in here that contains a single quote - such as the apostrophe in a word like "don't", then you must backslash (comment out) the single quote as well - eg: "don\'t" so that the PHP ignores it.
(Single quote marks are use by PHP for various programming purposes)
It's likely that most (if not all) of the php files that need editing will be in the LANGUAGES directories.
After making a backup of any php file FIRST (so that you can put the original back in place if you foul things up) CAUTIOUSLY make the edit to a couple of php files that appear to govern the description you want to change.
FTP the NEW file to your OVER-RIDES folder. DON'T overwrite the original one in the core directory. Make sure that if that file already appears in your over-rides folder, you could lose previous formatting by overwriting that file - in which case, just EDIT that file, don't overwrite it.
If you're not sure about over-rides and how they work, read up about this procedure first. (It's quite straight-forward).
USE A GOOD TEXT EDITOR - eg: CRIMSON EDITOR (free to download off the web). Don't use notepad, or the edit function that some c-panel interfaces provide.
And on the point of ftp - use a professional ftp program to send your files back to the server...