Make external backup of important documents, add new SSD, download Macrium Reflect Free, run from Windows and clone all of existing drive to new SSD, use disk management to expand the new C: volume if Macrium doesn’t automatically. Change boot order to new drive in the BIOS.
You might need another SATA data cable if you don’t have any spares. Should be spare power already.
If you’re on a laptop with only one HD slot, buy USB 3.0 2.5″ HD caddy and use that to clone then swap the drives.
Once you’re happy, old drive can be formatted and used for extra storage.
The other option is just move all documents to the new drive and keep the smaller one for OS and programs.