public enum VersionBaseType : System.Enum, System.IComparable, System.IConvertible, System.IFormattable  

public void ChangeVersions(Geodatabase geodatabase, string toVersionName)
{
  using (VersionManager versionManager = geodatabase.GetVersionManager())
  {
    VersionBaseType versionBaseType = versionManager.GetCurrentVersionBaseType();

    if (versionBaseType == VersionBaseType.Version)
    {
      Version fromVersion = versionManager.GetCurrentVersion();
      Version toVersion = versionManager.GetVersion(toVersionName);

      // Switch between versions
      MapView.Active.Map.ChangeVersion(fromVersion, toVersion);
    }

    if (versionBaseType == VersionBaseType.HistoricalVersion)
    {
      HistoricalVersion fromHistoricalVersion = versionManager.GetCurrentHistoricalVersion();
      HistoricalVersion toHistoricalVersion = versionManager.GetHistoricalVersion(toVersionName);

      // Switch between historical versions
      MapView.Active.Map.ChangeVersion(fromHistoricalVersion, toHistoricalVersion);
    }

    // Switch from HistoricalVersion to Version and vice-versa 
    // MapView.Active.Map.ChangeVersion(fromHistoricalVersion, toVersion);
    // MapView.Active.Map.ChangeVersion(fromVersion, toHistoricalVersion);

  }
}