All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and Messenger.
It is permissible for you to fold up your trousers before performing the prayer; as a matter of fact you are obliged to do so. It is forbidden to wear clothes that fall below the ankle even if the reason is not arrogance - according to a group of scholars. The Prophet, sallallaahu ‘alayhi wa sallam , said: "The lower garment should not be below the ankle." He also said to Jaabir Ibn Saleem : "Lift your lower garment until half of your leg [mid-shin]. If you cannot do so, then do not let it hang below the ankle. Beware of letting the garment below the ankle, as this is a sign of arrogance, and Allaah does not like arrogance." [Ahmed]
Furthermore, there is a narration which prohibits wearing clothes which fall below the ankle when performing prayer. Therefore, a Muslim should not let his garment hang below his ankle whether when performing the prayer or otherwise.
Allaah Knows best.