It's important to maintain your context-sensitive Help and keep topics in good working order. One of the ways you can do this is by removing obsolete map files.
Click the Project tab.
Open the Context-Sensitive Help folder.
Open the Map Files folder.
Click the map file you want to remove.
Click Delete
to remove the map file.
Click Generate
Primary Target to create an updated .CHM file.
Note: It is not a good practice to replace map files with new ones that use different topic IDs because you lose context-sensitive topics and aliases.