You can change this by going to "Appearance" > "Editor". Then look for the file "Home Page Template (home-page.php". Now you have to find the codes to make the changes.
For the "Choose Category" look for:
<?php /*?><iframe src="http://www.facebook.com/plugins/like.php?app_id=153282078076131&... bloginfo('url'); ?>&send=false&layout=button_count&width=450&show_faces=false&action=like&colorscheme=light&font=arial&height=21" scrolling="no" frameborder="0" style="border:none; overflow:hidden; width:100px; height:21px; position: relative; top: 1px;" allowTransparency="true"></iframe><?php */?></div></div><div id="content-upper" class="clearfix"><div class="heading-rest"><p>Choose a Category</p></div><p><select class="input_field" name="more-categories" id="more-categories"><option selected="selected" value="">Please Select...</option><?php
Find the section where it says "<p>Choose a Category</p>" and make sure to change just the wording and not to remove any of the HTML codes like <p></p> you see here.
For the "Search!" button, you need to look for this code:
?></select></p><p align="center"><input type="submit" name="submit" class="button set-c" onclick="redirecSelect()" value="Search!" /></p><?php
You should be able to spot the word "Search!" pretty easily and you can now edit it. Make sure to leave the quotes (" ") on and only change the wording.