To change the Character Set and Collation of a field of a table you have to use this query:
ALTER TABLE table_name MODIFY column_name data_type CHARACTER SET UTF8 COLLATE UTF8_UNICODE_CI;
if the table contains data, you have to update that data as follow:
UPDATE table_name SET column_name= CONVERT(CAST(CONVERT(column_name USING LATIN1) AS BINARY) USING UTF8)