VPS stands for ‘Virtual Private Server’ and is seen as a separate server by you and any other computer on the internet, but in reality it is actually a virtual environment hosted on a server with several other VPS.
They are seen by many as the step in between a cheap reseller account and a costly dedicated server – however, costs for VPS can vary greatly.
By having a VPS you have your own server, more or less, meaning that you can add programs and features as you like within your own environment without being at the mercy of other users; this can prove to be an advantage for some resellers since they might require special security settings which they’d never be able to get set on a reseller account – but which they will be able to set in a VPS environment.
A VPS is perfect for you if you require a dedicated environment but are not able to afford a dedicated server or if you have outgrown your standard reseller account and have no choice but to upgrade to a dedicated environment.
If you are using a control panel such as cPanel then you should be able to get all your data and websites moved over without causing any downtime or hassle to your customers.
See my list of recommended VPS hosting http://www.top10webhosting.com/virtual.php