Short comparatives, as pointed out previously, cannot modify nouns directly; they can only be used as predicates. One way to modify a noun is to place the по-comparative right after it. These comparatives usually have the meaning 'somewhat, a little, a bit'.
Add по to the short comparative and say it after the noun you're modifying.
Мнљ нџжен стћл побћльше/помљньше. I need a (somewhat) larger/smaller table.
Ї бы хотљл машќну полџчше. I'd like a better car.