Configure options unavailable?

I am trying to configure parallels to devote more memory to the virtual machine. however the options are grayed out under virtual machine>configure>hardware>memory. the slider is locked to 428 MB. Are there any options i need to enable before i can use this. Right now i am using the trial version, if that makes a difference. Im trying to test Heros of Newerth(beta) with parallels for the mac feedback forum there.

thanks

 

It does not matter. It's just that the virtual machine has to be stopped if you need to make any hardware settings change.