Hi Philipp Zykov,
For upgrading to 4.3.0, the documentation is not yet published. But you can read [this](https://gluu.org/docs/gluu-server/4.2/upgrade/) one, kind a similar process.
If you would like to upgrade using online script, then please use this one:
#### ***What is a best method - script or offline update via copying data?***
> It actually depends on the server. `Online upgrade using script` is the easiest way to upgrade the gluu server. We prefer to create a backup before going through the upgrade process whatever it's online/offline.
Regards ~ Shakil