Navigate to the client tab and click on the Custom Fields tab near the top of the screen to open up your custom fields menu.
Hover over the custom field you'd like to edit and click the open button to open it up.
Once a field is open, you can switch the sensitivity (only on text fields), edit the field name, add or remove options from your dropdown selections, or delete the field permanently.
Once you've made your edits, click Save Changes to update the field!