Is it true that a man get Moksha when he get rid of Tamas Guna ?
Or for getting Moksha , getting rid of all three Gunas is needed ?
Moksha requires the elimination of all 3 gunas.
Here is an excerpt from the Māhābhārata where Sage Sukadeva is described as discarding all the trigunas before he attains Moksha.
Having spoken in this way (unto all things), the regenerate Rishi of austere penances, viz., Suka, stayed on his success casting off the four kinds of faults. Casting off also the eight kinds of Tamas, he dismissed the five kinds of Rajas. Endued with great intelligence, he then cast off the attribute of Sattva. All this seemed exceedingly wonderful. He then dwelt in that eternal station that is destitute of attributes, freed from every indication, that is, in Brahma, blazing like a smokeless fire.
Getting Moksha requires a jiva to know the real nature of self - that is one with brahman. It has nothing to do with gunas. Gunas are intrinsic qualities that are bound to be present in a living being. Gunas can change from - sattava, rajas, or tamas, but still, it is bound to remain there [1].
In Advaita Vedanta, the self, under ignorance sees objects in the world with attributes and gets attached to them. Attributes mean - shape, color, size, age, etc. When the person is attached to something that is made up of certain attributes, he is said to be ignorant [4, 3].
When the same person treats - all shapes, colors, sizes, and ages as one and doesn't get attached to attributes or pained through it - he is said to be enlightened [4].
When the person is situated in self - his happiness/aversion to pain isn't dependent on external beings and through knowledge of Brahman (say - Vishnu/Krishna), he becomes one with it which is called Moksha [2,1].
When wise persons see that in all work there is no agent of action other than the three guṇas, and they know Me to be transcendental to these guṇas, they attain My divine nature.
The body - is supposed to contain three gunas - sattava, rajas and tamas in different proportions. When an enlightened man sees the body doing own work out of three gunas but doesn't identify itself from his actions of the body, but remains situated in self, attains the divine nature of Krishna.
2.
By transcending the three modes of material nature associated with the body, one becomes free from birth, death, old age, and misery, and attains immortality.
When the duer is not attached to the body, neither identifies with the operation of the body through physical self and knows real self (Atman), he becomes free from age, death, misery, as atman is free from all these.
3.
The Supreme Divine Personality said: O Arjun, The persons who are transcendental to the three guṇas neither hate illumination (which is born of sattva), nor activity (which is born of rajas), nor even delusion (which is born of tamas), when these are abundantly present, nor do they long for them when they are absent. They remain neutral to the modes of nature and are not disturbed by them. Knowing it is only the guṇas that act, they stay established in the self, without wavering.
When the gunas operate in the body, the self (atman), knowing free from all these - old age, death, misery, etc self should abide into the self and not get attached to the forms, shapes, and attributes that would lead to the real knowledge of self and prevention of attachment and pain. When a person who knows self successfully, he transcends the three gunas and death by situating in self and becomes one with Brahman (Krishna here).
4.
Those who are alike in happiness and distress; who are established in the self; who look upon a clod, a stone, and a piece of gold as of equal value; who remain the same amidst pleasant and unpleasant events; who are intelligent; who accept both blame and praise with equanimity; who remain the same in honor and dishonor; who treat both friend and foe alike; and who have abandoned all enterprises – they are said to have risen above the three guṇas.
Principal of Advaita - all forms, shapes, colors, designs, etc are delusion, and getting attached/pained through them leads to separation of self (Atman) through Brahman (Krishna), hence all attachment should be prevented to get situated in true self and get Moksha.
Sattva, Rajas, Tamas - all three gunas bind a person. Sattva is better, but it still causes bondage.
Bhagavad Gita
14.6 Of these (gunas), Sattva, being without impurity, is luminous and free from morbidity. It binds, O Arjuna, by attachment to happiness and to knowledge.
14.7 Know, O Arjuna, that Rajas is of the nature of passion springing from thirst and atttachment. It binds the embodied self with attachment to work.
14.8 Know that Tamas is born of false knowledge and deludes all embodied selves. It binds, O Arjuna, with negligence, indolence and sleep.
For moksha, getting rid of all 3 gunas is needed.
14.20 The embodied self, crossing beyond these three Gunas which arise in the body, and freed from birth, death, age and pain, attains immortality.