Starting with vSphere 6.7, there is no need to externalize the PSC for ELM, thereby making it simpler to protect vCenter Servers using vCenter High Availability (vCHA). However, if your existing environment has external PSCs, then upgrading them to vCenter 6.7 will retain the same topology.
With vCenter 6.7 Update 1, VMware includes a Convergence Tool, which can be used to install PSC components into existing VCSA 6.7U1 nodes and migrate the PSC configuration from the external PSCs into it, thereby getting rid of the external PSC nodes.
PSC 6.7 U1 (Windows) cannot be converted into embedded components of an existing vCenter. The Convergence Tools only work with vCenter and PSC Appliances.
At the time of the release of this book, the most recent version is vCenter 6.7 U2. Update 2 includes a GUI version of the Convergence Tool. However, the catch is that the source PSCs should also be running 6.7U2. For more details refer to VMware Tech Pubs demonstration - https://youtu.be/HlL4KzAPx0c