If you are having the access rights of workitem configuration, then you will able to add/remove workitem severity.
To add a workitem severity,
1. Click on Add Severity.
2. Give an appropriate name.
3. Select a system-generated icon.
4. Click on Save.
Users can delete any workitem severity. To delete any severity type click on Delete icon.
Severity Type Name:
Name the workitem severity, that you have added for instance: Major