Creo que para este caso, no hay nada más preciso que decir: "mejorar y/o actualizar" una determinada versión de software. Ver definiciones del portal lingüístico de Microsoft:
https://www.microsoft.com/Language/es-es/Search.aspx?sString...
"upgrade = actualización: A software package that replaces an existing version of a product with a newer and/or more powerful or sophisticated version of the same product. The upgrade process typically leaves existing customer data and preferences intact while replacing the existing software with the newer version."
"system upgrade =actualización del sistema: An upgrade of a system from an existing or older version to a newer or more recent version."
The translation workplace 
