I have read translation of a verse from Quran which I am not very sure about. I will be very grateful if you can clarify this for me.
"But if you intend to replace a wife by another and you have given one of them a Qintar (of gold, i.e., a great amount as Mahr bridal money), take not the least bit of it back; would you take it wrongfully without a right and (with) a manifest sin?" [4:20].
Does the above verse means that a man can divorce his wife just to marry another woman or if he has four wives he can divorce one of them to marry another woman?

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger. We ask Allaah to exalt his mention as well as that of his family and all his companions.

Allaah legislated divorce so that a husband would get rid of the wife he does not desire for sexual intercourse and whom it is impossible to live with for any reason, as He legislated for a wife to seek Khul' [ask for divorce in return for compensation] in order to get rid of her husband whom she could not live with for any reason as well. Indeed, this is a Mercy from Allaah for His Slaves, and He promised to enrich each [of them] from His provisions if they separate [by divorce], as this is better for them than living together in distress, suffering, unhappiness and troubles. Therefore, divorce is permissible due to the misconduct of the wife and her bad marital relationship and when being harmed by her, and the like. However, it is disliked to divorce without a necessity, for instance for the only purpose of marrying another woman, whether the husband has four wives or less. 

Allaah Knows best.