The HTML Help Registration tool allows you to replace a compiled Microsoft HTML Help file (.CHM file) in the registry with another one. This may be necessary if you have several versions of your .CHM file and want to replace an older version with an updated one.
Note: The process of replacing a .CHM file in the registry takes place on your authoring system and is not related to how users view your Help project after it's distributed.
From the Tools tab, double-click HTML Help Registration.
The HTML Help Registration dialog opens. The Name column displays the names of the .CHM files that are currently registered on your authoring system.
Select the .CHM file you need to replace.
Click Edit.
In Path,
click and navigate
to the drive/folder where the replacement .CHM file is located and double-click
to select it.
Click OK.
The Name column is updated to display the new .CHM file name.
To save the changes you made to the registry, click OK.
To cancel the changes you made to the registry, click Cancel.