Delete Tags in your account from the Tags page. When a tag is deleted it is removed from any person it's applied to.
To delete a tag from your account:
Go to People > Tags
Locate the tag you'd like to delete
Click the arrow next to the Edit button
Click I'm sure, delete this tag
If you add the same Tag name to your account, it will not reapply it to the people that had it before it was deleted.