After opening the 4.7 preview of the engine through the launcher you should be prompted when you double click on the current project. From this prompt you can choose to create a copy of the project in the engine version you are currently working in. This will make no changes to the current project (4.6.1) but instead recreate all of the projects assets as a new project. This way you can check out the features to come in 4.7 without having to worry about anything in the 4.6.1 version being affected.