(verb) to invalidate or reverse a law, prohibition or a ruling, etc.
"The European Court of Justice has overturned a ban on tobacco advertising across Europe."
reverse (reformar, reverter, estornar): "The decision was reversed on appeal." "We hereby reverse the trial court's judgment". -> reformamos a sentença; damos provimento ao recurso.
overrule (revogar, anular): "The Court of Appeal overruled the preliminary injunction granted by the District Court."
invalidate (invalidar): "Choosing to travel to a certain country against government or World Health Organization advice could invalidate a travel or health insurance policy."
affirm (reafirmar, confirmar, ratificar): "The court of appeal affirmed the judgment of the lower court."
uphold (manter): "The Supreme Court upheld the law permitting the distribution of campaign flyers on city streets on the grounds of freedom of speech."
"The Court of Appeal overturned the decision of the High Court."
"The judgment was overturned on appeal."
"His conviction was overturned after 5 years."
"The court overturned the ban on the new drug."
Overturn is a broad term that can refer to either a single act or a process; for example a series of court decisions can have the effect of overturning another decision.
Overrule is narrower and refers to what a higher court does when it abolishes a lower court's decision.