Hi Shantell, these are populated via flow steps in smart campaigns. If you need to find the specific campaigns that are attributing lead source, you can look at a lead's record and see which smart campaign updated their lead source. It might be a global campaign, or it could be local to each program.
Fortunately or unfortunately, there aren't any standardized values or standardized picklists for these values so they don't need to be amended by an admin.
In SFDC, have the admin edit the picklist related to Lead Source
in Marketo, you can insert ANY value you want, but ideally it should match the SFDC values. You might have these stamped on a Form as a hidden field, or like Dory said, a flow could be managing those.