I have started working heavily with VMWare at work and have setup my own HP DL380 G7 with VCentre 6.0 which needed 8GB of RAM. This was the smallest configuration available from VMWare however it was overkill for my home lab. This could be changed down to 4GB after it was shutdown and then reduced via ESXi web interface.
I decided to try VCentre 6.5 but unfortunately Vcentre 6.5 has higher memory requirements than version 6. I use Linux at home and VCentre 6.5 removes the need for the integration plugin and provides a faster HTML interface. The tiny instance has increased the RAM from 8GB to 10GB, I have plenty of RAM on my server however I didn't want to waste it unnecessarily. Unfortunately modifying it via VCentre is not possible as it refuses anything less than 10GB; shutting down the VC and modifying it via ESXi web host is also not possible as it fails with an error.
The only way I managed it was to use the Windows Vsphere Client connected to the ESXi host, this had no problem changing the memory; I guess that is because VMWare hasn't updated the client since the web interfaces came out.
This seems to work fine like it did before, the only thing to note is the hardware status is unavailable for the host with a message "No host data is available".
Hope this helps people.