King Louis the fourth decided to approve of a new constitution that stripped him of most of his power as a king. From there the Legislative Assembly voted on were to keep the monarchy or become a Republic which as you know already they'd decided to become a Republic. They then put Louis the fourth on trial along with his wife for treason because evidence was shown that he was dealing with foreign nations about counterrevolutionary planning behind France's back. Louis the fourth and the wife were executed by guillotine. Although the monarchy was offically abolished in France in 1792, for most it was after the death of France's final king.
Hope this helps :)