Converting from Lr to LrC

Simple....enable sync in the LrC catalog and all files already in the cloud will automatically download to your local hard drive and be added to the LrC catalog (and will contain all the edit info from the cloud). The issue is where and how they are organised in folders on the local system: to sort that out, BEFORE enabling sync in LrC, open the LrC Preferences>Lightroom Sync tab and you will find there the option to specify the location for the downloaded images (if you do not do that, LrC will use the default location which is an obscure folder in the user's AppData folder). There is also an option to have the downloaded files stored in one of LrC's standard capture-date based dated folder schemes. You would probably want to use both options to set things up as you would prefer, then you can enable sync.