Kwame Nkrumah declared Ghana's independence in:

Ghana gained independence from British colonial rule on 6 March 1957. Kwame Nkrumah, who had led the independence movement as head of the Convention People's Party (CPP), became the country's first Prime Minister upon independence.

Nkrumah had been a central figure in Ghana's struggle for self-governance since returning from studies abroad in 1947. He founded the CPP in 1949 after breaking away from the United Gold Coast Convention (UGCC), and his party won the 1951 and 1956 general elections. Under his leadership, the Gold Coast became the first sub-Saharan African country to achieve independence from European colonial rule, and it was renamed Ghana - after the medieval West African empire - to symbolise a new era of African self-determination.

The other dates are incorrect: 1955 and 1956 predate the actual independence, and 1958 postdates it. The year 1957 is one of the most significant dates in African history, as Ghana's independence inspired nationalist movements across the continent.