The best way to move an existing Windows installation, along with all of the installed programs, is to clone the drive. But cloning normally copies everything on one drive to the other. That doesn’t work if you have 800GB of files and only 120GB of new storage.
What you need is cloning software smart enough to let you pick what files and folders you don’t want on the new drive.
Such software might come with your SSD. But in my experience, bundled SSD cloning software leaves a lot to be desired. I haven’t tried every such program by a long shot, so if your new SSD comes with cloning software, give it a try. Of course, you’ll have to connect the SSD to your PC.
When the cloning is done, set your PC to boot from the SSD. Keep the old hard drive around, either in the PC or externally in a SATA-USB enclosure, for storing the files you exempted from the cloning and others that won’t fit on the SSD.