Userbenchmark does a decent job telling you the story, in this case.
You have an older processor, Certainly considered low end today.
You are using only hard drives, no SSDs. On some games this will have a big impact as it tries to load in game textures. 8GB of memory will hamper this as well. More memory, means more game files can be pre-loaded to RAM.
RX480 is a fairly old card. Still okay for 1080p, but certainly plenty of games that will crush it.
Windows has probably been on there for years, and you have probably have a lot of excess programs and files you aren't necessarily using. A fresh install of Windows may help. But if you were to do that, I suggest getting a small 240GB SSD for the boot disk.