Once you have given your interview and you know that what salary your are going to get i guess there should be no question after that . If you think that you deserve better salary then you could have tried in some other place where you would get a higher package. But once you are into it i would suggest learn things which you will be working in , there are huge opportunities are there where you can earn get good package with proper knowledge.
Asking your higher authority regarding increasing your salary on the day of joining or initial days are not a good option for you. It will tend to decrease your impression inside the firm.
Always remember learning had no end , if you can learn you work properly then there should not be any other option left for not getting the higher good salary package .