changing name of my movie source

That's not changing the name of your movie source, but it's changing the path in your video source. The source name is easily changed in Kodi.

There is no easy tool at the moment for changing paths in video or music sources. Perhaps some add-on can focus on that.

Right now, the Kodi database will store the full path to each video. Also, these full paths are stored in multiple locations in the database. It's not the most optimum solution, but it's what we inherited from the old days.

The long way would to do a full Video Library export, empty the video database, and reimport the video collection.

If your SQL knowledge is sufficient, you could execute a couple of SQL queries yourself directly in the database.

There is a tool that can alter the paths in the Kodi database, you can find it here. Always, make a backup of your database before you use the tool. No guarantees, it's not a fully tested add-on.