Je voudrais essayer cette robe dans une taille plus grande.

Pronunciation: zhuh voo-dreh eh-say-yay set robe dahn oon tye-yuh pluh grond.

Meaning: I would like to try on this dress in a larger size.

This polite request is essential when shopping for clothes in French-speaking stores; using the conditional "je voudrais" shows politeness and is more natural than the direct imperative form.