By using custom options you can Add/Edit values Test cases and Issues.
The Fields open for customization
Test Case
1.Type
2.Priority
3.Testsuite
Issues
1.Priority
2.Severity
3.Status
4.Operating Systems
5.Issue Version
6.Issue Type
7.Environment
1.To goto Custom option page,
Click on Administration->Custom Option
2.Enter the option label
3.Click on save button
1.Click on Edit option in the list
2.Update the details
3.To Disable the option choose the status as Disabled
4.Click on Save
1. To customize the options Click on Get Editable Options in Custom Option page
2. Now a copy of all existing option(s) of the field are available for you to customize
3. Click on Edit to Rename/ Disable the option