​Renewing through profex?
Start with this. It explains how to make your account and upload your initial information: http://www.mecd.gob.es/…/auxiliar…/PROFEX_MANUAL_2017-18.pdf
Then, there's a checklist on the website you have to physically check and mail in with the things you uploaded printed out.
Last, if you wanna stay at your school, have them do their part online, but there's also a form you give them to fill out and you upload in the "documentos anexos" part. 
If you follow that link, it goes step by step and it's actually not a bad process at all. You just need to fill out your info and upload basically everything you already have from CIEE


www.mecd.gob.es/eeuu/dms/consejerias-exteriores/eeuu/auxiliaresusa/PROFEX_MANUAL_2017-18.pdf