What I need to change is actually the tax description. In this tax, the description is currently VAT, but it should be IVA. In previous version of ERPNext (version 12), there was a button at the top of this form to change account name, but this is not possible in version 13.
@bahaou You are right! this was caused due to permissions. I connected as administrator and could make the change.
It is strange that both, Administrator and my own account, are “System User” and I compare permissions and they are the same. Do you know what specifically controls that kind of actions?