Please use this tricks carefuly because First trick will cause issue to your wordpress site.

First Trick
Improve the  wordpress Blog’s Loading Speed

WordPress, by default, comes uncompressed and sends the uncompressed HTML to the visitor’s browser.
Create one file called “phpinfo.php” and then upload it to the root of your blog directory:

In phpinfo.php fine copy paste following code.

<?php phpinfo(); ?>

Check on server zlib is enabled or not.

Copy paste the following code in to your header.php file above the Doctype tag.

<?php
ini_set(‘zlib.output_compression’, ‘On’);
ini_set(‘zlib.output_compression_level’, ‘1′);
?>

This trick will improve your speed upto 50%.

Code taken from following link :
http://www.wprecipes.com/compress-wordpress-output-and-speed-your-blogs-load-speed

Second Trick

Allow More Time For Slow Servers to Upgrade Wordpress

Open the wp-admin/includes/files.php file and go to line 448.

For WordpressMU users path is wp-admin/includes/file.php and line no 450.

Find this line
$response = wp_remote_get($url, array(‘timeout’ => 60));

replace with

$response = wp_remote_get($url, array(‘timeout’ => 120));

This will change the server response time to 120 second.

Code taken from following link :
http://www.wprecipes.com/wordpress-upgrade-allow-more-time-for-slow-servers