Either can be used.
spell1 /spɛl/ Pronunciation Key - Show Spelled Pronunciation[spel] Pronunciation Key - Show IPA Pronunciation verb, spelled or spelt, spell·ing.
–verb (used with object) 1. to name, write, or otherwise give the letters, in order, of (a word, syllable, etc.): Did I spell your name right?
2. (of letters) to form (a word, syllable, etc.): The letters spelled a rather rude word.
3. to read letter by letter or with difficulty (often fol. by out): She painfully spelled out the message.
4. to discern or find, as if by reading or study (often fol. by out).
5. to signify; amount to: This delay spells disaster for us.
–verb (used without object) 6. to name, write, or give the letters of words, syllables, etc.: He spells poorly.
7. to express words by letters, esp. correctly.
—Verb phrases8. spell down, to outspell others in a spelling match.
9. spell out, a. to explain something explicitly, so that the meaning is unmistakable: Must I spell it out for you?
b. to write out in full or enumerate the letters of which a word is composed: The title “Ph.D.” is seldom spelled out.