Steps to be followed for migrating lumen project to laravel

Probably easier to create a new laravel project and one by one moving the files from one project to the other.

Alternatively you should compare the composer files and then require the nescessary files and update

There is a Laravel shift for Lumen to Laravel.

Scroll a bit down on this page: https://laravelshift.com/

Laravel shift will give your repo pull request which you can merge, it also gives extra comments on the pull request for things you need to do manually.

Correction, its a pre-release so probably not yet available for everyone. See this tweet: https://twitter.com/laravelshift/status/833700056117215233

While an old post, the Lumen to Laravel Converter was release and still available.

If you're still running Lumen, I recommend converting as (IMHO) Lumen is "dead".