Java Heap Size Error

Question

i am basically building a movie reccomendation system with apache mahout, but i am using a 540MB dataset which occurs this problem in execution

  Exception in thread "main" java.lang.OutOfMemoryError: GC overhead limit exceeded
.
.etc..
.
  Picked up _JAVA_OPTIONS: -Xmx512m

So that i searched on web and learned that this is problem is coming from the heap size which you can see from the exception "Picked up _JAVA_OPTIONS: -Xmx512m" part , and i tried to change it in eclipse from -> run configurations ->Vm parameters but its not working so that i opened a command prompt in my class file path(File , Shift+Ctrl , Open Command Window Here) and i wrote these to change the limits minimum to 512 maximum to 1024

>java -Xms512m -Xmx1024m SuggestionMain

But this time , another exception occured which is below

Picked up _JAVA_OPTIONS: -Xmx512m
Error: A JNI error has occurred, please check your installation and try again
Exception in thread "main" java.lang.NoClassDefFoundError: org/apache/mahout/cf/
taste/model/DataModel
        at java.lang.Class.getDeclaredMethods0(Native Method)
        at java.lang.Class.privateGetDeclaredMethods(Unknown Source)
        at java.lang.Class.privateGetMethodRecursive(Unknown Source)
        at java.lang.Class.getMethod0(Unknown Source)
        at java.lang.Class.getMethod(Unknown Source)
        at sun.launcher.LauncherHelper.validateMainClass(Unknown Source)
        at sun.launcher.LauncherHelper.checkAndLoadMain(Unknown Source)
Caused by: java.lang.ClassNotFoundException: org.apache.mahout.cf.taste.model.Da
taModel
        at java.net.URLClassLoader.findClass(Unknown Source)
        at java.lang.ClassLoader.loadClass(Unknown Source)
        at sun.misc.Launcher$AppClassLoader.loadClass(Unknown Source)
        at java.lang.ClassLoader.loadClass(Unknown Source)
        ... 7 more

I couldn't understand and solve the problem here so can anyone help me to solve the memory problem?

Thank you for your help