E-goi's tags make it a cinch to segment your mailing list. But if you've already added tags to the list and would like to rename, delete or create new ones, just do the following:
1) Go to the "Lists" menu, head to the mailing list containing the tags you want to modify and click on "Contacts".
2) You'll be taken to a page displaying all contacts in that list. Head over to the left-hand "Tags" panel and click the gear-shaped icon.
3) You'll now be able to create, delete or rename tags - and even change their colour. Keep in mind this will reflect across the whole list! For example, if you rename a tag, the new name will be applied to every contact tagged with it.