Allah The Almighty does not accept any religion from the time Islam was revealed except Islam. Allah The Almighty Says (what means): {And whoever seeks a religion other than Islam, it will never be accepted of him, and in the Hereafter he will be one of the losers.} [Quran 3:85].
So, make haste to become a Muslim.
It is from the blessings of Allah The Almighty upon His slaves that He forgives all their past sins as soon as they becomeMuslims. Hence they become pure and clean as if they were just born.
Allah The Almighty Says (what means):
{Say to those who have disbelieved, if they cease (from disbelief) their past will be forgiven} [Quran 8:38].
{Say: "O My slaves who have transgressed against themselves (by committing evil deeds and sins)! Despair not of the Mercy of Allah, verily Allah forgives all sins. Truly, He is Oft-Forgiving, Most Merciful.} [Quran 39:53].
Embracing Islam is in reality acting upon one's Fitrah (natural disposition upon which Allah The Almighty created mankind). It is confirmed that the Prophet, , said: “Every child is born on the Fitrah.” [Al-Bukhari and Muslim]
Embracing Islam is a very simple process:
1. Utter The Two Testimonies of Faith, which is to say: "Ash-Hadu An-laa Ilaaha Illallaah Wa Ash-Hadu Anna Muhammadun Rasoolullaah" (I testify that none has the right to be worshipped but Allah and I testify that Muhammad is the Messenger of Allah).
2. It is recommended to take a ritual bath.
After pronouncing The Two Testimonies of Faith, one should be keen to learn how to purify themselves for prayer, how to pray, fast, and so on. This could be achieved by asking knowledgeable people, reading, listening to cassettes or CDs, or by visiting Islamic websites (like Islamweb: https://www.islamweb.net/en/). One may also visit local Islamic centers as they can be of great help.
A noteworthy thing to mention is that one does not have to proclaim The Two Testimonies of Faith aloud, and if one says this secretly to himself [without the presence of anyone] while acknowledging its content, then he/she is a Muslim.
Moreover, there are situations where a person fears that he might be harmed by others when they change their faith and revert to Islam, and thus saying this secretly would prevent others from discovering their reversion. It is not a condition that this declaration be said in front of the people or before a judge and so forth. Nonetheless, one should abide by the apparent religious rites, like the prayer and so forth.
After having entered the fold of Islam, one is advised to learn the matters pertaining to their religion, attend circles of knowledge held in Islamic centers and elsewhere, and be keen on keeping company with committed Muslim fellows so that they would help the new Muslim in doing good.
Finally, it should be noted that a person is ruled to be a Muslim by any of the following three things:
1- Uttering the Two Testimonies of Faith.
2- Having a Muslim parent, in case of children.
3- Performing the acts which are peculiar to the Muslims, like performing ablution, the prayer and so forth.