Skalp 2.0 replaces v1.2. Only one version can be installed on a SketchUp instance.
Currently v2.0 uses the exact same license as v1.2. => You can simply install v2.0 directly from the SketchUp preference window, using the regular procedure. No need to uninstall v1.2 first. No need to reactivate in this case. If you do need to active, you can use your original license activation code. Models using Skalp v2.0 can no longer be used on Skalp v1.2. So, for mission critical work, we advise you to store a backup copy of your model first. Migrating models from v1.2 to v2.0 on the other hand should be smooth and fully transparent.