Diffrent versions

If I purchased the previous versions, should I pay more in order to update to the current one?
If so, how much?

Are you talking about upgrading to current build from an earlier Visionaire Studio 4 build? or are you talking about from 3.7.1 to 4.1?

If you have already purchased one of the version 4 builds then all 4.x build can be downloaded with your current license. You only have to purchase a new license for when 5.0 comes out; well only if you want to upgrade to that, when the time comes.

From 3.5 (If I remember right, maybe it's 3.7.1) to 4.1.
should I pay the all sum to buy the new version or can I just upgrade the license for smaller sum?

there was only a reduced fee for people who bought the 3.7.1 license a short while before 4.0 was released. You will need to purchase the individual or multi license depending on your needs at full price, sorry.

How do I know which one do I need?
we are a group working on the game, but only one of us is using the engine, should I buy indivindual or Multi-user?

multi-user is based on developers, so the amount of people working in/with the editor should determine if you need an individual or multi-user license.