You can change the amount of RAM that a VM will use like this
memsize = "128"
If you don't assign a value for memory VMware will use the default-setting which is 32MB
memsize = "32"
Whenever you assign RAM manually make sure the value is a multiple of 4 - otherwise the VM will not start:
memsize = "255"
causes this error-message: Memory size 255 not a multiple of 4