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To increase the memory on the vCenter VM use one the below methods.
1) Connect to the ESX host on which VM is running using vSphere Client and then increase the memory on the vCenter VM
2) Connect to the ESX using PowerCLI and you can use Set-VM Cmdlets to set the Memory on the VM
Can you give me an example on alternative 2?
First connect to the ESX host using Connect-VIServer 'hostname'
Use this to set memory on the VM
Set-VM -VM "VMName" -MemoryMB "NewSize"
eg: Set-VM -VM VM2 -MemoryMB 512
Depending on your setup you should be able to add hot-add the memory to this VM while it's online. I typically do this hot, and always account for page file best practices which per Microsoft is still 1.5 x RAM, min and max (as opposed to System Managed). Make sure there is enough free disk space on the page file target, as part of your upgrade may involve expanding disks too.
Either way, I would try to get a reboot of this guest when possible to ensure everything is clean. You might also research the configuration of vCenter tomcat / java memory sizes for your deployment if appropriate.
This was extremely helpful. I just cannot figure out how to award stars.