Magento: PHP Extensions “zlib” must be loaded

Go to downloader/lib/Mage/Archive/Helper/File/ in your Magento directory

and edit the Gz.php file. You need to replace:

if (!function_exists('gzopen')) {

with

if (!function_exists('gzopen64')) {

and also:

"$this->_fileHandler = @gzopen($this->_filePath, $mode);"

with

"$this->_fileHandler = @gzopen64($this->_filePath, $mode);”