Should the injustices one faces be fought against in this world and to what extent should it be? Or should one not renounce ones rights and should make a complaint against the wrongdoers in the Hereafter?
One must avoid doing others injustice and must try to prevent others from doing injustice. This is a duty. Of course, there are Islamic criteria in eliminating the injustice done to us or to someone else. They must observe.
For instance, it is a command of our Prophet to prevent an evil or an injustice one sees with hand (actively preventing), if not, with tongue (verbally), and if it is also not appropriate/possible, then to answer it with the objection of heart. This hadith of the Prophet is explained by authorities as follows: To prevent the munkar (evil) with hand is the duty of the state and other authorities. And to prevent it with tongue is the duty of the learned and the people knowledgeable in that matter. Those who do not possess any authority, and who lack the knowledge to prevent the evil with tongue should hate it in their heart, in other words, they must object to that evil in their inner world.
Accordingly, when one is faced with an injustice, one must apply to the authorities for its removal, and if there are people capable of preventing the evil, one must let them intervene. And in cases when all these fail to prove successful, it means that the wronged person will get her/his right on the great Day of Judgment in the Hereafter.
As for renouncing ones right, it is a virtue; one may forgive the infringements on his rights if s/he wills. Those who prefer the way of forgiving when faced with an evil done by his Believer friend rather than retaliating with the same amount or more, will by all means receive the great reward of it in the Hereafter. However, their right to demand their rights is also guaranteed. It is up to the person to decide.