There is a MySQL table which has this definition taken from SQLYog Enterprise :
Table Create Table
You can change the default with an alter table set default charset but that won't change the charset of the existing columns. To change that you need to use a alter table modify column.
Changing the charset of a column only means that it will be able to store a wider range of characters. Your application talks to the db using the mysql client so you may need to change the client encoding as well.