If you are referring to changing boot order in the BIOS/EFI of the VM; couple of options
(1) in ESXi HTML5 UI client, edit VM settings, VM Options,
Boot Options - Force BIOS setup;
check the "The next time the virtual machine boots, force entry into the BIOS setup screen"
(2) add the line bios.forceSetupOnce = "TRUE" in the vmx file of the VM
This is the manual method of #1 above
I don't have vSphere Web Client so I don't have anyway way of checking, perhaps something similar exists there as the HTML5 UI client.
The bios.forceSetupOnce = "TRUE" works regardless the VM is on BIOS or EFI.
Hope that helps.
To reconfigure boot order you need to force the VM to enter BIOS setup on next boot.
Do this in the 6.5 vSphere Web Client, right click on the VM and select Edit Settings... from the context menu.
From the VM settings screen go to the VM Options tab and expand the Boot Options section.
Select the Force BIOS setup checkbox.