Converting .sb2 files to .sb3 format.
Converting Scratch 2.0 Project Files to Scratch 3.0 Project Files (.sb2 to .sb3 conversion) is certainly doable using the latest version of the Scratch software. There you should be able to load/import older .sb2 files, to then export them in the newer .sb3 format.
We are not aware of any third-party utility capable of directly converting .sb2 to .sb3 format.