You don't need to change the text in the psd file.
Just open the index.html HTML file and change the text.
Open the HTML in Notepad (TextEdit for mac) or any other HTML editor, don't open it in Word or any other rich text editor.
Example find this code:
HTML Code:
<div id="wrapper">
<h1><em>MUSIC</em> SHOP</h1>
and change it to:
HTML Code:
<div id="wrapper">
<h1><em>My own</em> shop</h1>
Save it.