I would first recommend upgrading vCenter to the latest 6.0 U3h. U1b is technically supported (review the below KB article from the interop matrix to ensure TLS is configured correctly) but was released over 2 years ago. Once that is complete upgrade ESXi to the latest Express Patch 19 (10719132).
VMware Product Interoperability Matrices
Unable to verify vCenter certificate in VMware View Administrator (2144967)
It's supported to upgrade from 6.2.4 directly to 7.7.0.
VMware Product Interoperability Matrices (Upgrade path)
You should upgrade composer and then immediately upgrading all of the connection servers in the pod. This can be done one at a time to keep the environment up and servicing connections. You will need to disable provisioning during the upgrade to avoid any composer/ad lds changes that could get out of sync. Then immediately repeat on the other pod (There have been some reports of CPA issues until both sides are running 7.7.0). Finally work through upgrading the Horizon Agents. As long as they are at least 6.2 they should continue to function but should be upgraded ASAP.
