Replace both sticks for 32GB

Yes, but you’ll need to swap out both 8GB sticks for two 16GB sticks.

With only two memory slots, you can’t just add more RAM. You have to remove the existing 2x8GB kit and install a 2x16GB kit. Selling the old RAM or keeping it as backup is fine, but mixing a 16GB stick with an 8GB stick would work (sort of) – it’ll run in single-channel or flex mode, losing some performance. Don’t do that.

Get a matched pair of 2x16GB. It’s a straightforward upgrade. Just check your motherboard’s supported speeds (usually DDR4-3200 or DDR5-whatever) before buying.

Future You deserves the full dual-channel bandwidth.