Unable to change email (Exchange ActiveSync) account (Android version 5.0.2)

I once had my professional email adresse setup on my android phone and it worked fine. For some reasons my account (on my workplace network) was deleted, and afterward re-set, but with a different login and password, but with the same email adresse. Now evidently the sync is no more possible on my phone du to those changes. But when I want to put the new informations I find that I can only change the account name, the password, the box for the SSL encrypted connection and the "select certificate" box, the rest being locked.

Does anyone know how I can unlock those parameters ?

P.S. For my gmail account I can change all the parameters.

Thanks in advance