This article explains well on how to upgrade an ESXi from 6.7 to 7.0. For me it didn’t allow as it was aking minimum ESXi version in the system as 7.0. But it allowed to patch from 7.0 to 7.0U3d patch. It was a great experience.
Source: How to Upgrade ESXi 6.7 to 7.0 by Using Multiple Methods