Zahoor,
The reason Kuroi gave you the link to read in the Wiki is that you need to follow some rules for templates. This is not a programming law. You can edit any file you want because it is your site and you own it. However, you should not do that.
The template override is THE BEST WAY to develop your cart. Before you customize too many things you should start a custom template.
This is the simplest tutorial in my opinion -
http://www.zen-cart.com/forum/showthread.php?t=7263 . This tutorial will tell you how to create a custom template and what files to edit.
While it takes a little longer to learn these basic principles and install a custom template, it is for your benefit in the long run.
Once you have that done, then editing for images and color can be done rather quickly. Again, the Wiki is very helpful. Search in the Wiki and read the instructions.
Best wishes.
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