First, check with the school to find out the latest that you can take the test. Most schools will let you take the test right up to the deadline. (They don't actually look at your application the day after you submit it. You'll self-report the score and test date, and then they'll just wait till it becomes available to verify that you really did score that.)
I'm suggesting this because you're looking for a 100+ point increase, and that is an unusual goal to achieve in 4 weeks (which is the time you said you had to spend).
If we can extend your timeframe to 6 to 7 weeks, then you have a better shot. It's still going to be tough, but you should aim for the 700 anyway, and if you don't quite make it, well, a score in the high 600s is still great too. :)
Next, we need to know your strengths and weaknesses in order to devise a study plan. Read this article:
http://www.beatthegmat.com/mba/2010/02/ ... study-planIf you've taken an MGMAT test in the past month and under official conditions (including essays), then do the analysis described in this article:
http://www.beatthegmat.com/a/2009/09/23 ... tice-testsIf you haven't taken an MGMAT test, it has been longer than a month, or if you took the test under very non-official conditions (skipping essays, taking longer breaks than allowed, etc.), then take an MGMAT test under
full official conditions (again, including essays). We're not going to be evaluating your essays, but writing for an hour can impact your multiple choice score, so you've got to do the writing first.
After you've done the analysis, come back here and post your results. We'll help you figure out what kind of study plan to set up based upon that.
While you're waiting, you should read these articles and begin to use the principles discussed:
http://www.beatthegmat.com/a/2009/10/09 ... ce-problemhttp://www.beatthegmat.com/mba/2010/04/ ... our-errorshttp://www.beatthegmat.com/mba/2009/12/ ... management