Houdini and Orbolt each support different ways of versioning assets. In Houdini, the version suffix is at the end. For example, your asset might be named:
    username::assetname::1.0
and you might come up with a new version named:
    username::assetname::2.0
To Houdini, these are two completely different node types. They can have different sets of parameters, and it is possible to have instances of each of the separate types in the scene. In other words, it is not necessary to chose which version is currently active -- Houdini treats them as two separate types of nodes.

This version is called the namespace version, and you can think of it as a major version number. The namespace version is completely optional, regardless of whether the asset is in the Orbolt store or not.

Within Orbolt is another version number. This one is just a number (1, 2, 3) and increments automatically every time you upload a new version of an existing asset. When you upload a new version, the users of that asset will use Houdini to update to the newest version. Each version posted to Orbolt must be backwards compatible with the old one, and must support the same set of parameters and the same functionality so that it can act as a drop-in replacement. A version can add new parameters and new corresponding functionality, though, as long as it doesn't break any scenes using old versions of the asset.

So, when uploading a new version of an asset to Orbolt, most of the time you are not changing the Houdini version number. If you need to change the parameter interface of an asset, or create a version that behaves differently (but better), changing the Houdini version number is a good approach. This will create a new asset in the store, and the previous asset (with the different version number) will still be around.