For anyone else who needs to run jforex in Windows with increased heap size but doesn't want to manually maintain a local copy of jforex.jnlp, in case it goes out of date, here is a batch file that downloads it and modifies the max heap size parameter on each launch:
@REM Use 'batch file parameter modifiers' to first change current directory to where this batch file resides
%~d0
cd %~p0
del .\jforex.jnlp
"C:\Program Files (x86)\GnuWin32\bin\wget" --no-check-certificate https://www.dukascopy.com/client/demo/jclient/jforex.jnlp
.\ssr 0 max-heap-size=''512m'' max-heap-size=''4096m'' jforex.jnlp
javaws -J-Djnlp.client.username=DEMO2OMDAa -J-Djnlp.client.password=OMDAa .\jforex.jnlp
It requires: