VPS

 
I want to buy a VPS, I've already bought one, but I don't check one thing, for example, I buy one for server A, can I then change VPS to server B? or do I have to buy another one for server B?

For example from Metaquotes server to FTMO server,
 

Yes, if you subscribe to MQL5 VPS, you can change the trading account is assigned onto, once a week.

https://www.mql5.com/en/vps/subscriptions