npm update is not updating the version in package.json file

I am trying to update specific package in my project. I have checked it using npm outdated and then I run this command to update this package: npm update nameofpackage i.e., npm update slugify.

My package.json file is not got updated after that, although when i run npm outdated again it shows no outdated package. It means it got updated but my package.json file still shows the older version of the package.

Please let me know how can I update my package.json file also. I have tried npm update slugify --save also but it didn’t worked for me.