I am using MacBook Pro (15-inch, Early 2011) the problem is I can't see any update to newer version on App Store! Can anyone here send me the link to update online or download updates to next version.. I am very new user.
The highest version of macOS you might be able to run is High Sierra - why not download that installer or try sierra?
As commented - we have several questions on how to download specific versions if that’s the thing that’s blocking you.