As WonderVM stated, the Virtual Machine that Virtual Center is running on is using hardware version 10, which will not allow him to update the memory settings without using the web client.
IMHO he has 3 options:
Edit the .vmx file to change the memory settings.
Use standalone converter to change the hardware version back to version 8 or 9, then complete the memory upgrade.
Create a new Virtual Machine as version 8/9, configure the correct resources, then attach the vmdk's.