Sorry for the delay.
You will have to convert the data in the tables as well as changing the collation of the tables. There is information here to do that: http://en.gentoo-wiki.com/wiki/Convert_latin1_to_UTF-8_in_MySQL. You will only need to do the conversion if you were storing old non-UTF8 data in the tables. If you have been only storing UTF8 data in non UTF8 tables, then chaning the collation of them will be all you need to do. Note - make backups of your data before attempting any of this!
You may want to check the settings for the default collations for your database. Most add-ons don't specify a collation, so it depends on this setting when the tables are created.
mike