A forthcoming 4.5 release will allow customers to upgrade existing 4.0 cluster to 4.5. Please refer to release notes for allowable upgrade paths.  The 4.5.070 is only for net new cluster installs.
Does anyone knows when the VxRail 4.5.070 upgrade becomes available for VxRail 4.0.302/4.0.400 customers? It would be released in Q4 2017. It's now almost 2018 and it's still not available for download.
VxRail 4.5 upgrade for VxRail 4.0 customers