How do I find custom fields?

I have a custom field in a webform that a developer made for us that lists names of who the potential lead spoke with. I need to update that drop down list on the webform, but everytime I try to do so, I only can change the title not the drop down list names. Where do I go to find the custom field to modify it?

Goto Admin → Settings and click the ‘Go’ button like in image below:

Find your field and click edit. From there make changes and save: