[totaltec]

You are looking for /include/product_tabs.php.

After line 54:
$product_tabs = array();

The sections below this define the individual tabs, just change the order that they appear in the document. Move the code block that represent "Send to Friend" below the others. This is the send to friend block, line 111 on my system:

if ($config['Appearance']['send_to_friend_enabled'] == 'Y') {
    $product_tabs[] = array(
        'title'  => func_get_langvar_by_name('lbl_send_to_friend'),
        'tpl'    => 'customer/main/send_to_friend.tpl',
        'anchor' => 'send2friend'
    );
}