Magento version: 1.4.2
XAMPP version: 3.1.0
PHP version: 5.4.7

If you can still log into Magento’s backend, you can easily modify the base URLs of the site via:

System -> Configuration -> Web (Under the General section) -> Unsecure

There change the Field "Base URL" to the new domain.

System -> Configuration -> Web (Under the General section) -> Secure

The "Base URL" field should match the site’s domain.

But, if you cannot access the backend anymore, you need to modify the URL within the database thru phpMyAdmin if you have one configured.

Find the table "core_config_data" then click the Browse tab and edit the first two fields:

web/unsecure/base_url
web/secure/base_url

The last thing you need to do is clear the Cache. The Magento cache folder is located in your Magento installation directory > /var/cache. To clear the cache, delete the folder and create it again.

Visit your website, if in case you receive this error after deleting the Cache folder, Can't retrieve entity config: core/store_group, then do the following:

  • Replace lib/Varien/SimpleXML folder of Magento 1.4.x with the same folder from magento 1.6-1.7.

The error happens due to outdated SimpleXML library that is not compatible with PHP 5.4.