There are many ways one can repent. First by completing the daily prayers, every sin committed between them is forgiven. By attending the Friday Jum'ah prayers, the weeks previous sins are forigiven. By fasting the month of Ramadan, the sins of the past year are forgiven. By completing the pilgramage, all sins committed in the past are forgiven and one returns like a new born child. A person who converts to Islam as all of their previous sins forgiven since they were committed without knowledge. By completing the optional tahajud night prayers, one can be forgiven for all of their sins.
Allah loves to forgive the sins of his servants as one of His names is the most forgiving and another is the most merciful. The only requirement for being to be forgiven is that they be sincere in repentance with the intention of never repeating the sin, though we being human as we are doesn't always happen. In this case Allah forgives again and again as He tells us in the Quran.
The Quran has dozens of verses describing Allah's mercy for those who repent and how they should repent. Here are a few verses translated from the Quran:
Allah accept the repentance of those who do evil in ignorance and repent soon afterwards; to them will Allah turn in mercy: For Allah is full of knowledge and wisdom.
( Chapter #4, Verse #17)
But those who do wrong but repent thereafter and (truly) believe,- verily thy Lord is thereafter Oft-Forgiving, Most Merciful.
( Chapter #7, Verse #153)
But (even so), if they repent, establish regular prayers, and practise regular charity,- they are your brethren in Faith: (thus) do We explain the Signs in detail, for those who understand.
( Chapter #9, Verse #11)
But (even so), if they repent, establish regular prayers, and practise regular charity,- they are your brethren in Faith: (thus) do We explain the Signs in detail, for those who understand.
( Chapter #9, Verse #11)
But any that (in this life) had repented, believed, and worked righteousness, will have hopes to be among those who achieve salvation.
( Chapter #28, Verse #67)
O ye who believe! Turn to Allah with sincere repentance: In the hope that your Lord will remove from you your ills and admit you to Gardens beneath which Rivers flow,- the Day that Allah will not permit to be humiliated the Prophet and those who believe with him. Their Light will run forward before them and by their right hands, while they say, "Our Lord! Perfect our Light for us, and grant us Forgiveness: for Thou hast power over all things."
(Chapter #66, Verse #8)