I’ve been meaning to do this for some time so here goes.
Some time ago I had a customer who was still on venter 6.5u2d.
We had to update the vCenter as part of a vSAN upgrade and thus had to start with the vCenter. To do this upgrade there are a couple of things to be aware off.
1: You will need an extra IP address and fqdn to be created for the upgrade.
2: The old vCenter will be transferred to a new appliance.
3: The upgrade is as always in two stages.
4: This example is with an already integrated PSC. I would recommend having that done before starting to upgrade to vCenter 7.
5: Please also make sure you check compatibility for the upgrade. In our case we were on 6.5 u2d and we could at the time only go to 7.0.2. 7.0.3 was avaialable back then but had a bug so it was recommended to stay clear of that until a new version was released.
6: You need the firstname.lastname@example.org and root password(s) for this upgrade (also for the esxi your vCenter is staying on).
7: Disable drs to avoid the vCenter moving anywhere during the upgrade.
8: Do not forget to take a backup of the database and or the vCenter. I do actually suggest to create a clone so you have a vm you can go to in worst case.
9: I do suggest to have an open Support case with VMware so they are aware of that you are doing something and can have resources available to jump on a call in case it is needed.
Once these steps are done, you can continue to the actual upgrade. You can find those steps here.