In most writing scenarios, the general consensus is that different from is a better choice than different than.
Why? No idea.
Just kidding.
The word from is a preposition, so all it needs is an object (a noun or a pronoun). The word than signals a dependent clause, so, technically, it needs a subject and a verb in order to be considered complete. Confused?
Let's take a look at an example sentence:
After his friendly chat with the snake in the zoo, Harry knew that he was somehow different from the rest of his class.
If we subbed than into the sentence, it would read he was somehow different than the rest of his class. Though the sentence sounds correct, it should technically be he was somehow different than the rest of his class was. If you plug from into the sentence, you have no need for the extra verb.
With that being said, if the sentence you're looking at does have a clause, feel free to use different than. That works just fine.
But as a general rule, you should stick with different from. It's clean and simple.