If a Muslim does sins that puts him beyond the pale of Islam for which he becomes kafir mushrik and murtad how can he repent and does he have to do ghusul and repeat kalimah shahadatayn and will his repentance being accepted or what are the steps so that he can again enter Islam and become muslim
Answer:
In the name of Allah, the most Beneficent, the most Merciful.
Generally speaking, the opinion of the Ahlus Sunnah Wal Jamaat is that a sin, irrespective of how grave or heinous it may be, does not take a person out of the fold of Islam. (Dars Muslim p.202 v.1)
Therefore, regarding your question, a sin how grave it may be will not take you out of the fold of Islam. However, if you did commit a sin or crime which may have taken you out of the fold of Islam, then say the following sentences:
“I bear witness that there is no God but Allah, and I bear witness that Muhammad, (Allah bless him & give peace), is His servant and Messenger.”
“I have believed in Allah and His angels and His book (as they were originally revealed on His prophets) and in His messengers and in the Last Day and in the fact that all the good and bad destinies come from Allah and in being raised alive after death.”
A man called Amr Bin Aas 
came to the Prophet of Allah 
and said, “Give me your right hand so that I may give you my pledge of loyalty.” The Prophet stretched out his right hand. Amr withdrew his hand. The Prophet of Allah said: “What has happened to you, O Amr?” He replied, “I intend to lay down a condition.” The Prophet of Allah asked: “What condition do you intend to put forward?” Amr said, “That Allah forgives my sins.” The Prophet of Allah said: “Didn’t you know that converting to Islam erases all previous sins?” (Sahih Muslim p.76 v.1)
Finally, in the Hanafi Fiqh it is considered desirable for a person accepting Islam to perform a ghusl. It is only when the person accepting Islam is in an impure state (i.e. in the state of janabah) does ghusl become compulsory. (Nurul Idah p.60)
Only Allah Knows Best
Mohammed Tosir Miah
Darul Ifta Birmingham.