Replace the HDD with an SSD first.

It will make a much bigger difference than doubling the RAM.

An SSD is the single biggest speed upgrade you can make to an old laptop. Your computer isn’t slow because it’s running out of memory—it’s slow because it’s waiting on the hard drive to load everything. Even basic things like opening a browser or launching a program take forever because the HDD is the bottleneck. An SSD fixes that immediately. Everything feels snappier.

8GB RAM is still fine for most everyday tasks—browsing, Office, streaming, light photo editing. Unless you’re running a dozen heavy apps at once or trying to play modern games, 8GB is enough. If you do upgrade RAM later, you’ll get a smaller boost for more money. A decent 500GB SSD costs about the same as a 16GB RAM kit (maybe less), but the SSD will transform the machine.

The one exception: if your laptop has soldered RAM and you can’t upgrade it later, and you know you need more memory for specific work. But even then, the HDD is the bigger pain.

Do the SSD first. Your laptop will feel new again. Then worry about RAM if you actually run out.