How to increase java heap space

I get the following exception when I try to upload a file (33MB) with a webservice in ivy 4.3.21:

org.apache.axis2.AxisFault: java.lang.OutOfMemoryError: Java heap space at org.apache.axis2.util.Utils.getInboundFaultFromMessageContext(Utils.java:486) at org.apache.axis2.description.OutInAxisOperationClient.handleResponse(OutInAxisOperation.java:343) at org.apache.axis2.description.OutInAxisOperationClient.send(OutInAxisOperation.java:389) at org.apache.axis2.description.OutInAxisOperationClient.executeImpl(OutInAxisOperation.java:211) at org.apache.axis2.client.OperationClient.execute(OperationClient.java:163) at devd3.d3wservicegen.D3WServiceStub.ImportDocument(D3WServiceStub.java:14234) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source) at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source) at java.lang.reflect.Method.invoke(Unknown Source) at ch.ivyteam.ivy.webservice.restricted.exec.axis2.WebServiceCallAxis2.invokeMethod(WebServiceCallAxis2.java:687) at ch.ivyteam.ivy.webservice.restricted.exec.axis2.WebServiceCallAxis2.executeCall(WebServiceCallAxis2.java:454) at ch.ivyteam.ivy.webservice.restricted.exec.axis2.WebServiceCallAxis2.perform(WebServiceCallAxis2.java:258) at ch.ivyteam.ivy.webservice.restricted.execution.WebServiceCallBean.executeAxisWebServiceCall(WebServiceCallBean.java:239) at ch.ivyteam.ivy.webservice.restricted.execution.WebServiceCallBean.perform(WebServiceCallBean.java:355) at ch.ivyteam.ivy.process.engine.internal.io.extension.ProcessExtensionJob.run(ProcessExtensionJob.java:298) at ch.ivyteam.ivy.process.engine.internal.io.extension.ProcessExtensionThread.runAsSystem(ProcessExtensionThread.java:271) at ch.ivyteam.ivy.process.engine.internal.io.extension.ProcessExtensionThread$1.call(ProcessExtensionThread.java:219) at ch.ivyteam.ivy.security.internal.SecurityManager.executeAsSystem(SecurityManager.java:1404) at ch.ivyteam.ivy.process.engine.internal.io.extension.ProcessExtensionThread.run(ProcessExtensionThread.java:214)

Is there a simple way to increase the java heap space or is there any other solution available to upload bigger files? A file with 24MB can be uploaded without any problem. The webservice would support MTOM and excepts the file data as an javax.activation.DataHandler object.