Sell the old RAM if you can get $30+ for it.

Sell it.

RAM is one of those PC components that almost never fails. Keeping a spare 16GB kit “just in case” is usually overkill—you‘ll likely never need it, and by the time you do, it’ll be obsolete anyway. The money from selling it now is more useful than a dusty stick sitting in a drawer.

Check eBay or r/hardwareswap for recent sold prices. If your kit is DDR4-3200 or faster and in decent shape, you can probably get $30–50. That pays for a nice dinner or a game. If it’s DDR3 or low-speed DDR4, you might only get $15–20, at which point I’d keep it for a backup or build a secondary machine.

One exception: if you have a second computer that could use the upgrade, or if you’re planning to build a test bench, keep it. Otherwise, let it go.

Future you will appreciate the $40 more than the box of old gear.