From the fact that you are using the H5 client and not the Flex client I am going to assume that you are a tenant rather than the Cloud admin and you are asking about your particular OvDC.
assuming you have Admin rights in your OvCD.
power off the VM That you are wanting to change the compute resource one
select the virtual machine and select details. this will load a new form.
in there are for sub sections
Guest OS Customization
the bits you need will be found in the Hardware section
my bad. I misread your question - increasing Video memory is not available via the H5 client to my knowledge,
well please let me know if it's possible via the flex client
Couldn't find it either. Maybe check the API if it is possible. As a workaround we have changed video memory settings on the master image via vCenter.
Nor unfortunately is it available from the Flex client either. it could be available via the API but I have not tried it.
No this is not available at all in the vCD API. One needs to go directly to vSphere for this.