My iMac and my MacBook Pro had been running out of memory and disk space for some time now.
After some research online, I found that, even though a hard drive replacement in a MacBook is risky, I could handle it myself. It was fun to buy the screwdrivers and the components. I like doing manual work now and then. Aside from a short, tiny scare, it all went smoothly, and I enjoyed seeing the bowels of my machines.
Now they are ready to serve comfortably for another few years.
PS: If you’re looking to replace the hard drive on your MacBook Pro, here are instructions.