6.5 is a high score. If your English is very poor, it would take many months of study. However, in one month of very hard study, our full course can help you gain at least one band (if not more).
It is hard to say whether you can achieve large gains in just one month (this depends on the person), but you will definitely improve your chances of receiving the score you want!
If you want to work on your writing and get some feedback, make sure you take advantage of our editing services!