How do I I migrate from rails 3.1.4 to rails 4.2.6

See more:

Ruby

Rails

im trying to upgrade my project from ruby 1.9.3 to ruby 2.3.0, and the rails version from rails 3.1.4 to rails 4.2.6 , after updating my gem files, i get an error "Bundler is using a binstub that was created for a different gem.". What should i do?

What I have tried:

I tried bundle update, then ran the command "rake rails:update:bin
", but as soon as i run rails server,, it complains about concat being an undefied method, yet its defined.