1) Before you move make sure you sign-up with your new mambo hosting company.

This will enable you to migrate your existing mambo site to the new hosting provider without the risk of downtime. it also give's you a good opportunity to test the new web host facilities like support, speed and reliability before you make the big move.

2) Another benefit to signing up to a new web host is to avoid
   downtime plus the risk of loosing your search engine ranking. If you move to a new web host and the migration is not complete the search robot's could index the content of your new web site which is not fully migrated, developed.

3) Backup your Mambo MySQL database and your directory contents.

Once you have completed the backup migrate, upload it to your new web hosting provider. The old site will be still available but you can fully test the new web site migration to ensure it works. before moving to a new server please visit the official mambo forum for hint's and tip's.

4) Once you have moved to the new mambo hosting company, the migration was a success and everything works well. It's time to make the change by visiting your domain registar where you will need to make a change to the " name server " entry. The name server entries maybe something like ns4.yournameserver.com
Once this is complete it can take up to 24/48 hours for the new change to come into effect. Once the new changes are in place everything will point to your new web hosting site.