I am being hired as an intern for a company, and parking will be $177/month. They say they will reimburse me for $90. But I am almost going to have a masters degree, so I feel like maybe I can get more. But how do I politely ask for more?
If the standard employee allowance is $90, e.g that's the allowance given to everyone in the company, you are unlikely to be successful, although asking for double the allowance because you're already making considerably less as a intern (if that's true), might be something the company would do. In case, you would simply say "thank you for extending the employee allowance to interns as well, but is there any way to get more since my salary is less than that of a regular employee?"
However, if that is the allowance given only to interns, or you are not receiving a considerably smaller salary than an entry-level employee, or if you are receiving other benefits as an employee that are not typically given to interns, then I probably wouldn't push your luck. There's a fine line between looking too demanding and needy versus actually being needy.
If you cannot get to work any other way besides driving and parking, and you cannot afford to make up the difference on your own, then you might want to consider a cost-benefit analysis of taking that position in the first place.