Changing web hosts becomes a necessity when your site becomes popular, & your current host is unable to meet your needs. You then need to find a host that can offer you a higher level of scalability and more services.
You should plan the movement carefully. The first step, of course, is finding a new host. The second is making the switch. However, before you make the switch you must take a back up of all your data. The back up should be saved in the original directories, so that you don't have to do fresh database planning.
However, if your website is not properly structured then this is a good time to have a professional redesign the database. You will find that good database management brings in scalability.
For the first 48 hours, you should use a redirection page on your old host to ensure that you don't loose traffic. After that, the new IP address will be listed on most domain name servers on the net, and your visitors will not face any hardship reaching your site.
Here are some more tips that can make the transition easier:
Find out in advance if your new hosting service uses a Windows or a UNIX operating system to ensure that it is compatible with your present hosting package.
Make sure that your new host supplies sufficient storage space - and can add more GBs as and when needed.
Find out if your new host provides facilities such as auto responders, e-mail accounts and mail forwards. These are minor services but they make your site more professional.
Does your old host use FrontPage? If your new host uses FrontPage, is it the same version?
Be sure that your new host can release extra bandwidth as an when the traffic spurts on your site.
If case of shared hosting, make sure that your new host does not host adult sites. These sites corner large chunks of bandwidth. Your site, as a result, becomes slow.
You should also check the past experience of your new host. Avoid going to companies that have just set up new hosting companies.
Once your files have been uploaded on the new server, make sure that the new website functions properly. Most hosts provide a preview link, to enable you to see how your website looks, before the domain name is transferred.