
(There is a "Migrate" option when you run the VCSA installer.) Windows vCenter Server must be v5.5 or v6.0 (any build/patch) to migrate to vCenter Server appliance 6.5.
vCenter Server on Windows is no longer available in vSphere 7, so any previous versions must be converted via the assistant. vCenter 6.0 or later can be directly upgraded to 6.7. vCenter 5.x cannot be directly upgraded to 6.7 an intermediate upgrade to 6.0 is required (see above.). This one is easy, since from here you can easily upgrade to 6.5, and then 6.7.
vCenter 5.5 or later can be directly upgraded to 6.5 or U1. So, if you still have vCenter Server 5, make sure to upgrade it to vCenter 5.5 first. vCenter 5.0 or 5.1 with updates cannot be directly upgraded to 6.5 an intermediate upgrade to 5.5 or 6.0 is required. Please note that some of those versions are no longer supported by VMware.
We can sum the vCenter version and upgrade possibilities into five major points. Deprecated topologies and vCenter upgrade paths ^
Before you upgrade or migrate your environment to vSphere 7, you must move any deprecated deployment topology to a supported deployment topology.