Delete a label in Jira
You can get rid of labels that are not needed anymore in your Jira environment. If you just want to rename or merge the duplicate labels, please refer to this page Rename labels in Jira instead.
To delete a label globally:
Go to Apps → Manage Labels
Find the label and click Delete. A confirm window will open, click OK.
If you have a label that is used in too many issues, this operation might take a while.
To delete a label only in a project, go to Project → Manage Labels instead.

Delete a label in Jira
Sometimes deleted labels are still suggested in label field, please refer to Known Issues & limitations for workaround.