Upgrading RavenDB instance to a new version is very simple. In order to do so, you:
Shutdown the RavenDB server. (This is depends on your deployment strategy. For a service - shutdown the service. For a IIS site - shutdown the IIS site.)
Replace the binaries (including any bundles if you have them, their version has to match the server version).
Make sure to not delete your actual data which is the folders like data or tenants, or overwrite your configuration files like Raven.Server.exe.config or web.config.
Start the server again.
On a live system, this process typically takes 30 seconds, which is fast sufficient in most cases.
However, if you want zero downtime, you can setup a failover server which will handle requests until the primary server is started up. The steps to do so are:
When you setup the primary server, you have to make sure to that it has the Raven.Bundles.Replication assembly in the plugins folder.
Setup a second server, with the Raven.Bundles.Replication assembly in the plugins folder.
Setup a replication between the primary server to the second. (Modify Raven/Replication/Destinations document to point to the secondary server).
Wait until the second node will get all the docs from the primary node (but a minimum of 10 minutes, to make sure that any clients had the chance to get updated with the new replication information).
Shutdown the first. You're now silently failover by the clients to the secondary server.
Replace the binaries of the first and start it again.
Shutdown and update the secondary server.
Stable file formats
You don't have to do anything when you upgrade RavenDB to migrate the stored data. However, sometimes we perform changes which require changing the file format. RavenDB include support for perform those kind of migrations automatically on startup if it finds that the stored database is using an old format.
Please note, however, that those migrations are only one way. If you want to move backward and a change to the file format have occurred, RavenDB will fail to start (with a detailed error message). You can move data between different versions using the import/export tool, which works across all versions of RavenDB.
If you have the secondary node running only for the during of the actual update, you don't need a license.
If you have the secondary node running constantly (hot backup), you do need a license.