IIRC once the installer asks you for a Key/Product-ID just click 'skip this step' and the system should automatically activate once connected to the internet.
Windows 10 licensing is per machine so if you already have a legit and activated license for that PC all you need is the installation media which is freely available from this Microsoft website. If you would rather reinstall from scratch:
Otherwise there are free cloning utilities available but I haven't used any recently so can't offer suggestions. The SSD probably comes with a cloning utility, either with a CD/DVD (if it came with one) or downloadable from the manufacturer website. You have a couple of options, you can clone the installation onto the new SSD, install it as the primary boot drive, then wipe the old drive once you're sufficiently convinced everything works OK, or you can just fresh install Win10 on the new SSD and copy over the old files you want to keep, install your software from scratch, etc.
