In short: facing a denial (or silence, which in immigration is usually negative) you can appeal: a reposición appeal (1 month) before the same body and/or a judicial review (contencioso-administrativo, 2 months) before the courts. Deadlines are short (Law 39/2015).
In person or by representative? Administrative appeals can be filed through a representative (a lawyer or authorised person), and even via the electronic register; they do not require personal appearance (legal standing and representation: Instruction SEM 1/2024).
Administrative silence: in most immigration procedures silence is negative (if they do not answer in time, it is understood denied). You can request a certificate of administrative silence and appeal with it. (Important exception: in renewals silence is usually positive.)
Available appeals:
- Reposición appeal (optional): before the same body that issued the decision, within 1 month of notification. The body has 3 months; if it does not decide, it is deemed rejected and the judicial route opens.
- Alzada appeal: before the higher body, when the act does not end the administrative route.
- Judicial review (contencioso-administrativo): within 2 months of the notification of the denial (or from the silence deadline).
Recommendation: deadlines are short and non-extendable; it is advisable to consult an immigration lawyer to choose the route and prepare the appeal.
Official source: Law 39/2015 on Common Administrative Procedure (arts. 123-124 for reposición).
Informational only; the route and deadlines depend on the specific act — check the official source and a professional for your case.