is it Ustedes or ustEdes ?? (capitalized word being the emphasized word)
Words ending in a vowel, n, or s have the stress on the next-to-last syllable. uSTEDes
Words that end in a consonant other than n or s have the stress on the last syllable. uSTED
An accent (sometimes called a tilde) always gets the stress and is used to "break" the two rules above.