I am really confused about this. I know that men should keep the bottom of their pants above their ankles, so I fold my pants. But I have heard that it is not right to fold your pants and some say you have to fold your pants or your salat will not be accepted. I don't know what is right, so can anyone tell me the detail about why we should or should not fold our pants.
This is an issue on which scholars have differed. The vast majority of scholars throughout time claim that folding of cloth is makrooh? I already told that this type of question should be off topic.?
It is offensive to draw together ones clothing [including pants] during the prayer, by folding or tucking them up for example, or to enter the prayer with ones garment like this. The proof of this is the prophetic tradition: "I have been ordered to prostrate on seven bones and to neither gather a garment nor hair." The wisdom behind this is that it prevents the clothing and hair from prostrating along with one and it is an appearance which does not conform with submissiveness and humbleness.
As for the hadith 'whatever is below the ankles is in hellfire', the reason was because in their times it was done out of haughtiness, and that surely isn't the case in the west. Allah knows best.
 Related by Bukhari and Muslim [No. 490].
 See: Ibn Hajar al-Haytami, Hawashi al-Sharwani Wa Ibn Qasim al-Abbadi 'Ala Tuhfah al-Muhtaj Bisharh al-Minhaj (Beruit, Dar Ihya' al-Turath al-'Arabi)
Check out for more info: http://sunnaforum.com/index.php?/topic/3559-salah-issues-regarding-folding-before-salah/
As far as I know, it is fine to fold the trousers if it is done neatly. If it is not done neatly, then it is makruh (disliked).
In the name of Allah, Most Compassionate, Most Merciful, In terms of the validity of the prayer, there is no question that performing Salat with trousers folded up does not invalidate one's prayer.
As for this being disliked (makruh) in Salat, it was explained in a previously posted answer titled: 'Wearing Short-Sleeved Shirts' that the Hanafi jurists (fuqaha) generally consider performing Salat in ways that are contrary to proper etiquettes (adab), such as rolling-up one's sleeves to the elbows, to be Makruh. (Radd al-Muhtar, 1/ 640)
In light of this, it will be Makruh to perform Salat with one's trousers folded-up if they are folded in an untidy and improper way, such that one would feel embarrassed to be in that state in noble gatherings; for example folding the trousers up to or close to the knees. However, if they are folded neatly and slightly, then it will not be Makruh.
As for the Hadith recorded by Imam al-Bukhari in his Sahih from Sayyiduna Abdullah ibn Abbas (Allah be pleased with him) that the Messenger of Allah (Allah bless him & give him peace) said, 'We have been ordered to prostrate on seven bones, and to neither gather a garment nor hair' (Sahih al-Bukhari 777), it refers to lifting or gathering and tying one's garment from the front or back before going into prostration (sujud) to prevent it from touching the floor. This is prohibitively disliked, as it goes against the spirit of Salat which is based on ultimate humility. (See: Imdad al-Fattah sharh Nur al-Idah P: 357 and Tahtawi ala Maraqi al-Falah P 350)
And Allah knows best