Dear Support Team,
at gibbon update time, I am replacing all files with old version, so my custom code & css are change.
is there any solution I can updating only some files not all files.
This can be tricky. The best way to preserve changes between update is to create a GitHub account (if you don't already have one), then fork the GibbonEdu/Core repository. From here, you can commit your changes to a branch, and then every time there is an update you can merge the new version into your branch. This will help you maintain your changes and manage any conflicts that arise. It's a bit of a technical process to get setup if you've never used git before, but it's definitely the best way. You can find a lot of information online, and theres some tips for getting started in our contributor guide:
The other option is to keep a log (in a spreadsheet or document) of all the changes you make and to which files, then manually merge your changes back into the new version with each update.