There are many, many legacy Microsoft Access databases that need to be supported and enhanced. Often the original developer is long gone and there's little to no documentation available.
Yet, you're expected to take care of it.
No matter what technology it is, taking over someone else's work is always challenging. It's even more challenging if you become responsible for a system that you (and no one else) understands.
FMS President Luke Chung explored this topic during his presentation at the Portland Oregon Microsoft Access User Group Conference. Learn about the issues and techniques we've learned over the years to triage, enhance, and support Microsoft Access applications, including migrating and upsizing to SQL Server and other platforms.
Here's a paper and PowerPoint presentation: Tips and Techniques for Taking Over an Legacy Microsoft Access Database Applications