The command I needed was:
wmic memorychip get speed
This showed the speed of the internal 4GB RAM to be 2400.
I installed this:
Crucial CT4G4SFS824A 4 GB (DDR4, 2400 MT/s, PC4-19200, SRx8, SODIMM, 260-Pin) Memory,
and this has brought the system up to 8GB and everything seems stable.
I do not...