Drinks are 'standard' size. Whatever size glass the restaurant uses for that type of beverage is the size they'll serve your drink in. If juice always comes in a six ounce glass, that's what you'll get. If soda glasses are 16 ounces, that's how they'll serve your soda.
Of course you can ask for a larger glass, but there's no guarantee you'll get it - or that if you do, it will be covered by your meal credit.