If you are referring to the very old Lightroom 3.6, and not the cloud-based Lightroom, then it will be necessary for you to first install the trial version of Lightroom Classic long enough to use it to upgrade your catalog. The upgrade process will create a new copy of the catalog, leaving the old version intact and accessible by Lightroom 3.6. Then you can have Lightroom 4.1 access that upgraded catalog to migrate all the images to the cloud. The folder structure will not be the same. The cloud system does not use the familiar folder structure. Your images will be imported by date, and then you can organize them into albums.