i often changed the values for RAM/CPU, this makes no problem.
Just take a look at your VmWare Server if there are enough ressources free. If now, your performance will degrade even you bump the MWG system ressources.
You are saying that the performance will still degrade even after increasing the resources? Does this mean the MWG OS is ignoring the increase in resources and using only those resources which were present at the time the virtual appliance was originally built?
You should be able to increase VM resources without a problem (no need to recreate the machine).
I think Thorsten is saying that you should check your virtual machine host first? And if it doesnt have enough you'll have problems.