Is Shirk Forgivable?
Question

I would like to know if Allah will forgive somebody who has done shirk knowingly but wants to change his ways for good forever pls it is very important and another thing how can such a person be forgiven and know that he is forgiven and how can a person increase his iman and do the things that are halal and avoid haram plus be void of psychological problems because I have a lot of them and they bring a lot of confusion and anger and lead me astray thank u pls i am very desperate for guidance from Allah in the form of a person.
Praise be to Allah.Is Shirk forgivable?
Allah has told us that he will forgive all sins for the one who repents to Him. He says (interpretation of the meaning): 
“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’” [Az-Zumar 39:53]
This includes all sins, even Shirk . Whoever repents, Allah will accept his repentance . 
How to repent from Shirk
With regard repentance from Shirk in particular and the acceptance thereof, Allah says (interpretation of the meaning): 
“And those who invoke not any other god along with Allah, nor kill such person as Allah has forbidden, except for just cause, nor commit illegal sexual intercourse and whoever does this shall receive the punishment. The torment will be doubled to him on the Day of Resurrection, and he will abide therein in disgrace; Except those who repent and believe (in Islamic Monotheism), and do righteous deeds; for those, Allah will change their sins into good deeds, and Allah is Oft-Forgiving, Most Merciful.” [Al-Furqan 25:68-70] 
Allah mentions the disbelief and Shirk (associating others with Allah) of the Christians, then calls them to repent. He says (interpretation of the meaning): 
“Surely, disbelievers are those who said: “Allah is the third of the three (in a Trinity).” But there is no god (none who has the right to be worshipped) but One God (Allah). And if they cease not from what they say, verily, a painful torment will befall on the disbelievers among them. Will they not turn with repentance to Allah and ask His forgiveness? For Allah is Oft-Forgiving, Most Merciful.” [Al-Ma’idah 5:73-74] 
No matter how great the sin, the forgiveness, generosity and kindness of Allah is greater. 
All you have to do is to turn to Allah , regret what you did and resolve not to do it again. Then receive the glad tidings of the bounty and mercy of Allah, for Islam wipes out whatever sins came before it, as the Prophet (peace and blessings of Allah be upon him) said to `Amr ibn Al-`As (may Allah be pleased with him): “O `Amr, do you not know that Islam wipes out whatever came before it.” (Narrated by Muslim, 121 and Ahmad, 17861) 
And the Prophet (peace and blessings of Allah be upon him) said: “The one who repents from sin is like one who did not sin.”  (Narrated by At-Tirmidhi, and classed as sound by Al-Albani)  
If a person repents to Allah, Allah accepts his repentance and forgives him. Allah says (interpretation of the meaning): 
“And He it is Who accepts repentance from His slaves, and forgives sins.” [Ash-Shura 42:25] 
“And verily, I am indeed forgiving to him who repents, believes (in My Oneness, and associates none in worship with Me) and does righteous good deeds, and then remains constant in doing them (till his death.)” [Ta-Ha 20:82] 
We have to think well of our Lord and hope that He will accept our repentance, for Allah says, “I am as My slave thinks I am.” (A Qudsi Hadith narrated by Al-Bukhari, 7066 and Muslim, 2675) According to Ahmad with an authentic chain of narrators:  “I am as My slave thinks I am, so let him think whatever he wants.” 
How to strengthen faith
With regard to strengthening your faith , this may be done in many ways, such as the following: 

Remembering Allah a great deal, reading His Book and sending a great deal of blessings upon His Prophet (peace and blessings of Allah be upon him). 
Regularly offering the obligatory prayers on time and offering a lot of optional prayers, so that one may attain the love and support of Allah as it says in the Hadith: “Whosoever shows enmity to someone devoted to Me, I shall be at war with him. My servant draws not near to Me with anything more loved by Me than the religious duties I have enjoined upon him, and My servant continues to draw near to Me with supererogatory works so that I shall love him. When I love him I am his hearing with which he hears, his seeing with which he sees, his hand with which he strikes and his foot with which he walks. Were he to ask [something] of Me, I would surely give it to him, and were he to ask Me for refuge, I would surely grant him it.” (Narrated by Al-Bukhari, 6137) 
Keeping company with good people who will help you to worship and obey Allah and discourage you from disobeying Him.  
Reading biographies of righteous people among the scholars, ascetics (Zahids), devoted worshippers and those who repented. 
Keeping away from everything that reminds you of sin and calls you to it. 

In general, faith is increased by doing acts of worship and keeping away from prohibited things. 
We ask Allah to help you and to accept your repentance, and to guide your heart. 
And Allah knows best.