Hey I have found a link which is giving an info over the procedure for migrating to a new web hosting account without downtime....check it out:
Please respond whether its a working or not, or just something is missing..
actually, it depends on the web hosting provider you're moving to. A good, experienced company will do the migration for you without downtime and mostly free of charge, as my host did for me
It is very simple, follow this below procedure and you can migrate your hosting without a single minute of downtime..
1) First, do not switch your Name Servers until you move all the data to the new provider.
2) Pack all your website files and Database from old provider.
3) Move it to the new provider and restore the databases and change the Db details in the necessary DB settings file.
4) Make sure the new moved website is working fine with your temporary URL, you can ask your web hosting provider to give temporary access URL with which you can check whether everything is working fine or not.
5) Final step, if everything is working fine, simply switch your name servers the new provider.
That's it, you won't face even a single minute of downtime, also it doesn't depend on a web host, actually it depends on you how you do that. Cheers!
I'll do shuk one better: Use cPanel's move a website feature to change host (both hosts must use cPanel). That's the fastest and cleanest way to relocate because cPanel can move ALL your settings to the new host (db, mail, ftp, as well as your website). Just be sure to wait 72 hours (after changing the DNS pointer to the new website) to allow propagation (as stated above and, yes, this is critical).
Generally migrations with control panels similar at both ends goes smooth. It entirely depends upon the hosting company/individual who carries out the migration. Also make sure that you have a recent copy of backup before the start of migration.
I would use the cpanel method to do the move.