the add to cart button trigger is at line 147:
if (isset($_POST["skincentrics_1_ATC"]) || isset($_POST["skincentrics_1_ATC_x"])) {
change that to:
if (isset($_POST["KT_Insert1"]) || isset($_POST["KT_Insert1"])) {
NOTE: you will also need to merge the add to cart form elements into the registration form
change the following code:
<input type="submit" name="KT_Insert1" id="KT_Insert1" value="Register" class="eC_FormButton" style="background-color:#d4a67c;" />
</div>
</form>
<!-- Confirm Form -->
<form name="skincentrics_1_ATC_22" method="POST" action="<?php echo $_SERVER["PHP_SELF"]; ?><?php echo (isset($_SERVER["QUERY_STRING"]) && $_SERVER["QUERY_STRING"] != "")?"?".$_SERVER["QUERY_STRING"]:""; ?>">
<input type="hidden" name="skincentrics_1_ID_Add" value="22" >
<input type="text" name="skincentrics_1_Quantity_Add" value="1" size="4" >
<input type="submit" value="Add to Cart" name="skincentrics_1_ATC">
</form>
to:
<input type="submit" name="KT_Insert1" id="KT_Insert1" value="Register" class="eC_FormButton" style="background-color:#d4a67c;" />
</div>
<!-- Confirm Form -->
<input type="hidden" name="skincentrics_1_ID_Add" value="22" >
<input type="text" name="skincentrics_1_Quantity_Add" value="1" size="4" >
<!--<input type="submit" value="Add to Cart" name="skincentrics_1_ATC">-->
</form>