Muhammed himself answered this when he said that a better revelation was revealed.
Koran 2:106
Ibn Jarir Al-Tabari (d. 310 H.) said:
Allah means with (Such of Our revelations as we abrogate): we abrogate the ruling of a verse by another to change and replace this ruling. This is by making Halal to become Haram and vice versa or to let what is permissible to become impermissible. Thus, abrogation is only concerned with matters of commands and rulings such like: permissibility and impermissibility, prohibition and Halal
etc. Therefore, previous nations news and stories have no abrogation
[Tafsir Ibn jarir (jamie Al-Bayan):1/521]
Ibn Kathir said as well: Ibn Abi Talha narrated Ibn Abbas saying: (Such of Our revelations as we abrogate) means: what we replace of verses.
Ibn Jarir reported from the way of Mujahid: This part means: the verses we erased and Ibn Abi Najeh from the way of Mujhaid narrated Mujahid said: we confirm the verse and its place in Quran but we replace its ruling. This is what the companions of Ibn Masoud narrated as well. [Tafseer Ibn Katheer: 1/207]
Al-Qurtubi in his book Al-Jamie Li Ahkam Al-Quran while he was talking about the verse of abrogation:
Having knowledge about this matter is needed and its benefit is great, to the extent that all scholars need to know about abrogation because only the ignorant would deny abrogation since abrogation is needed to know the rulings of what is Haram and halal [Al-Jamie Li Ahkam Al-Quran: 2/61]
2) {And when we put a revelation in place of (another) revelation, and Allah knoweth best what He revealeth they say: Lo! thou art but inventing. Most of them know not.} [Al-Nahl: 101]
Ibn Jarir Al Tabari said:
Allah the exalted says: We abrogate the ruling of a verse by replacing it with another ruling in another verse. In regards the part where it says {And Allah knoweth best what He revealeth}; Allah says there: what Allah abrogates and replaces is for the best of benefit to his creation as He knows the best. The part {revealeth they say: Lo! thou art but inventing} means: those, who associate someone with Allah in worshiping and disbelieving in the messenger, say to the messenger: O Muhammad you are inventing this which means that you claiming that Allah said that while he did not. So Allah replies to what they said: indeed, most of them are ignorant about the fact that what you Muhammad- bring them i.e. abrogated verses and verses that abrogate another verse are all from Allah.
Scholars of interpretations said exactly as what we said about the above verse. And some of those who mentioned that are: [..chain of narration..] Mujahid said about this verse: it means Allah lifts up a verse and replace it with another
[..chain of narration..] Mujahid said: Allah abrogates verses, replace them , lift them up and confirm another verse in abrogated verses.
[..chain of narration..] Qutada said: the context of the verse {. as we abrogate or cause to be forgotten,} is same as {we put a revelation in place of (another) revelation}.
[.. chain of narration ..] Ibn zaid said about the part where Allah says {we put a revelation in place of (another) revelation}: they; disbelievers, said to Muhammad you bring something then you say otherwise. So Allah says: this replacement is an abrogation because whenever a verse is replaced by another then it has to be an abrogation. [tafseer Ibn Jarir: Jamie AlBayan: 7/646] and for further readings: Ibn Katheer: 2/774] and AlJamie Li Ahkam AlQuran by Al Qurtubi: 10/157]
I took this resarch from a Moslem discussion site
here