How to get Previous & Next Product Buttons on Product view Page in Magento

To implement Previous & Next product button you have to edit view.phtml file which is located in:
app/design/frontend/your-instance-name/your-theme/template/catalog/product/view.phtml
If you not found view.phtml there then go:
app/design/frontend/base/default/template/catalog/product/view.phtml
Now open the view.phtml with any code editor. If you want to insert Previous & Next product button after the Product Name as me, then find the following code (line no:49 in version-1.5):
<div class="product-name">
    <h1><?php echo $_helper->productAttribute($_product, $_product->getName(), 'name') ?></h1>
</div>


<?php // Previous and Next product links in product page
$_product = $this->getProduct();
if(!$_product->getCategoryIds())
return; // Don't show Previous and Next if product is not in any category
$cat_ids = $_product->getCategoryIds(); // get all categories where the product is located
$cat = Mage::getModel('catalog/category')->load( $cat_ids[0] ); // load first category, you should enhance this, it works for me
$order = Mage::getStoreConfig('catalog/frontend/default_sort_by');
$direction = 'asc'; // asc or desc
$category_products = $cat->getProductCollection()->addAttributeToSort($order, $direction);
$category_products->addAttributeToFilter('status',1); // 1 or 2
$category_products->addAttributeToFilter('visibility',4); // 1.2.3.4
 $cat_prod_ids = $category_products->getAllIds(); // get all products from the category
$_product_id = $_product->getId();
$_pos = array_search($_product_id, $cat_prod_ids); // get position of current product
$_next_pos = $_pos+1;
$_prev_pos = $_pos-1;
 // get the next product url
if( isset($cat_prod_ids[$_next_pos]) ) {
$_next_prod = Mage::getModel('catalog/product')->load( $cat_prod_ids[$_next_pos] );
} else {
$_next_prod = Mage::getModel('catalog/product')->load( reset($cat_prod_ids) );
}
// get the previous product url
if( isset($cat_prod_ids[$_prev_pos]) ) {
$_prev_prod = Mage::getModel('catalog/product')->load( $cat_prod_ids[$_prev_pos] );
} else {
$_prev_prod = Mage::getModel('catalog/product')->load( end($cat_prod_ids) );
}
?>
 <div>
<?php if($_prev_prod != NULL): ?>
<a href="<?php print $_prev_prod->getUrlPath(); if($search_parameter):?>?search=1<?php endif;?>"><span><?php echo $this->__('PREVIOUS PRODUCT') ?></span></a>
<?php endif; ?>
<?php if($_next_prod != NULL): ?>
<a href="<?php print $_next_prod->getUrlPath(); if($search_parameter):?>?search=1<?php endif;?>"><span><?php echo $this->__('NEXT PRODUCT') ?></span></a>
<?php endif; ?>
</div>