I converted my main app some years ago. It took a few days and I wrote it up here:
The main thing is to be careful and systematic and take it bit by bit. DO NOT just select the menu option “Convert tthis project to API2”. Work from the bottom up. A project can perfectly well be a mixtture of API 1 and API2. Do you use any Text or Xojo.xxx stuff? I dumped all that even earlier than API2 appearing. If you do, you might want to convert that first.