It is same, you can use both.
The difference is not easy to explain. In many case you can use "an" and "année".
You just have to be careful of the use, because "an" is male and "année" is female, so it belongs with the gendre of the word it will be attached.
Example :
- l'année prochaine / l'an prochain (same for dernière/dernier)
Generally :
“An” a unit of time (ex: j'ai 15 ans)
“Année” is more the continuance (C'est ma deuxième année d'école.)
After you have the exeptions, some expression that you have to use like that :
- le jour de l'an
- toute l'année