Install LR CC, open it and select your catalog, it will prompt you to make a "new" catalog compatible with CC and your done.Your old catalog can still be opened with LR 5.7 if you want. I assume if you save out and read in .xmp sidecar files, any changes in one version will show up in the other (without any history). Only challenge there might be if you've used a brush on a graduated or radial filter, which LR 5.7 doesn't handle.