You've got a VPS, 4 accounts, 4 EAs, and don't know how to install an EA?
Go to your MT4 Help file and follow the instructions there. Make sure to start with a demo account so that you can be sure that the EA is functioning correctly.
If you want to trade 4 different accounts, you will need 4 instances of MT4. If you want to trade 4 EAs on one account, you can probably do that with one instance of MT4. Overall, I don't recommend running more than 1 EA on a single account unless you are very sure of what you are doing.