You are able to edit the content on your custom dropdown field by following the steps below:
1. Open your Sitefintiy backend
2. Go to Administration -> Module Builder
3. Open your module
4. Click the name of the module under
This module contains...
5. In the Fields of this item section find your field and click it.
6. The you will have the ability to change the content of the field.
For your convenience I have recorded a sample video demonstration
the Telerik team
Do you want to have your say in the Sitefinity development roadmap? Do you want to know when a feature you requested is added or when a bug fixed? Explore the Telerik Public Issue Tracking
system and vote to affect the priority of the items