Following up on Installing Debian Linux I decided to replace that machines’s hard drive by a 500GB SSD. This went quite smoothly. The only hitch was that the 3.5″ SSD mounting bracket for the 2.5″ SSD did not have any any screw holes to match those in the space left behind by the old 3.5″ drive. So I ended up securing it with duct tape!
I also had to reinstall Debian. The free edition of Macrium did not have an obvious way to transfer the Debian partition from its external USB drive to the new internal SSD, even though there was plenty of space. I expect this can be done, but I did not have the knowledge. I could have left Debian on the USB drive, but the new SSD had space for it and I have too many USD devices hanging off that machine anyway.