SCORM Source Files/Articulate

Hi.  I'm switching vendors and have gotten all my SCORM course packages from them (the courses were created in Articulate).  However, I know I need the source files in order to ever be able to make edits to the content in the future.  I have a few questions that I just can't seem to find the answers to:

- What are the source files actually made up of?  Are they the actual Articulate presentation that the vendor created?

- What do you do with the source files once you have them?  Can you simply open them in Articulate, edit them and then republish them? 

Many thanks for any input!