Set Memory Limit without using Launcher

Hi all,
I've been having trouble, like others,installing xmage through the launcher due to java not found, have manually downloaded the correct java etc but just getting a black DOS screen.
Loading from the client is fine but am stuck on 512 memory which is causing lag.
Is there a way to set the memory limit by using the client and not the launcher?
Thank you
John
I've been having trouble, like others,installing xmage through the launcher due to java not found, have manually downloaded the correct java etc but just getting a black DOS screen.
Loading from the client is fine but am stuck on 512 memory which is causing lag.
Is there a way to set the memory limit by using the client and not the launcher?
Thank you
John