Question maybe someone can help????

Ok I have Microsoft outlook 2003 for email. Now here is the dilemma, when I had dial up I had to limit the size of incoming mail because it would take forever! Now I just would like to change it from 2.5MB incoming to unlimited and well of course I can not find it anywhere!!!!

Can anyone help please, I have searched on line and my question is not getting answered and well I am getting frustrated!!!!!???????????????????