You have the ability to edit a source by clicking the 3 dots next to the source on the Sources page and choose the option that says Edit.
The Edit Source page gives you the option to rename the source. It also provides allows you to edit the filters that have been applied to a given source. If you need to change the actual URL or handle of the source, you will need to Archive it and re-add it.
*Note - to archive a source, you will need to click the same three dots that allow you to edit and choose the option that says archive.