A segmentation can be deleted by following the steps below.
1. Go to the Database.
2. Go to your segmentation and click on Used By to check associations.
If your segmentation is used by other assets, remove all those associations before you proceed.
3. Remove all associations and then in Segmentation Actions click Unapprove.
You can remove associations by deleting or creating alternatives for the assets that use the segmentation.
4. Once unapproved, click on Segmentation Actions and Delete the segmentation.
That's it. You can't get it back, so make sure you don't need it anymore.