Non-European citizens entering the country through a border that is not subject to control and coming from another Member State of the EU are required to declare their entry within three days (Article 14 of Law 23/2007 of 4 July last, changed by Law No. 63/2015).
If you enter Portugal by air you must declare entry at the airport near the Customs Service. In case of renewal of the length of stay, it will be necessary to schedule a meeting; that which can be done online through this website. It is extremely important that the student be aware that the renewal of the visa should be treated at least one month in advance.