Usually, the hosting where you are migrating should offer you such service to move your website for free or you can contact their support for a paid service of site migration that should not cost more than 10 dollars.
Yet, some of you might want to move a website 'with your own hands' and to know what you did if further migration would be needed once.
The most important thing while moving your site from an old to a new web hosting is that your visitors should not see anything unusual is going on.
It means zero downtime and that can be achieved.
The key to a zero downtime web site migration is that you have access to a both of servers, the new one and the old one at the same time for a few days.
First thing you should do is to download and backup all of your files from an old server and then to upload them onto a new one.
After that you only need to set up your Hosts file in Windows and temporary redirect your web site domain to a new server than set up the website there and update DNS information when you are done.
After updating DNS information for a domain name do not delete the website from an old server immediately, wait for a few days and then perform a final deletion.
A more detailed information about editing hosts file in Windows XP, Windows Vista and Windows 7 can be found here: http://www.
gt1987.
com/2010/01/how-to-move-website-to-another-server-without-any-downtime-editing-hosts-file-in-windows/