Our noble Prophet Muhammad (SAW) said: “At the beginning of every century Allah will send to this ummah someone who will renew its religious understanding.”

As for “(one) who” in the hadith quoted above, it may refer to one person or more than one person. Thus, the one who will renovate the religion for us may be one person or a group of people or a party. Anyway, Muslims are not to wait idle for that person or group of persons; they are to seek individually and collectively to renovate the religion themselves.
The eminent Muslim scholar, Sheikh Yusuf Al-Qaradawi, states: “The hadith quoted was reported by Abu Dawud in his Sunnan and Al-Hakim in his Al-Mustadrak.
This hadith is a ray of hope that breathes life into the Muslim Ummah and urges it to give up despair and have faith that Almighty Allah will not leave it an easy prey to weakness, deterioration, and disintegration. Almighty Allah raises for this Ummah from one century to another one who helps it unite and revive and awaken it to its responsibility in this life. These are some of the meanings that renovating religion according to the hadith refers to. Renovating religion indicates reviving the Ummah through understanding its religion very well and guiding it to the right path.
The majority of the scholars of Hadith believe that “who” in the hadith refers to one person on whom Allah has bestowed moral, scientific and scholarly characteristics that help him revive the religious teachings and give them momentum. He is to do this through contributing to true knowledge, doing good deeds, or leading the Muslims in a great jihad in Allah’s cause.
Hence, many scholars tried to specify the person who renovated the religion at the end of each of the previous centuries; they sometimes agreed on that person and some other times did not. For example, they agreed that the renovator at the end of the first century was `Umar ibn `Abdul-`Aziz, known as the fifth Rightly-Guided Caliph; that in the second century it was Muhammad ibn Idris Ash-Shafi`i; and that in the fifth century it was Ibn Daqiq Al-Eid. But they greatly differed with regard to specifying the renovators of the other centuries.
In my point of view, “who” in this hadith and in general may refer to one person or more than one. Thus, who can renovate religion in each century is not necessarily one person; it may be a group of people. This may include scholars, governors, leaders, teachers, etc. They may be in one country or in a number of countries. Each of them may work on his own, or they may cooperate with one another through an association or a society. They can work in more than one field; some may renovate in calling to Islam, some in culture, some in jurisprudence, and others in the field of education and pedagogy, social reform, or economic and political spheres, etc.
The most important thing in that respect is that the participants in this process be keen to coordinate on what to do and strive cooperatively to fulfill it, not to work individually in a way that may impede the work of the others, for this may weaken them all and make their enemy stronger.
To confine renovation in religion to one person makes people live in the hope of his emergence, doing nothing but waiting for him to fulfill what they are not able to do. This is why people do wait for Al-Mahdi (a person about whom Allah’s Messenger gave the glad tidings that he will guide the Ummah to the right path).
Anyway, I see that renovation of religion is to be the aim of Muslims, whether they are groups, schools of thought, or movements. Each Muslim zealous for his religion is to take part in this aspect and do as much as he can to serve that aim. Hence, the question is not who is to renovate our religion, but, rather, it should be what can one do to renovate the religion?”