Updating demands a lot more of the server than the regular day-to-day work.
It’s always a good idea, and sometimes essential, to have swap. If you can spare the disk space, 4G swap is a good number.
I have in the past temporarily upsized my server to more RAM, done the upgrade, then downsized it. You have to sure this is reversible. It only costs a few pennies to run the bigger server for an hour or so. But of course, there is a little downtime with this method.