PC Master Race

I'm not very tech savvy so please bear with me.

I bought a premade in 2018 and I've only updated the graphics card and ram since then. I'm using a 55" Samsung TV as a monitor. It's really starting to get sluggish/finicky. Gaming example: it can run BGate3 on medium but starts having issues any higher.

• Processor: Intel Core i3-8100 Coffee Lake CPU, 4 Cores, 3.6GHz
• Graphics Card NIVIDIA GeForce GTX 1070 8gb
• CPU Cooler: Intel Stock CPU Cooler
• Motherboard: ASUS Z370-P Motherboard
• Memory: 8GB DDR4 2400MHz Memory (2 x 4GB Sticks) + Crucial Ballistix BL2K8G36C16U4B 3600 MHz, DDR4, DRAM, Desktop Gaming Memory Kit, 16GB (8GB x2), CL16, Black
• Hard Drive: Seagate 2TB Firecuda Hybrid Hard Disk

EDIT for more info

It's hooked up to my TV because I use it for everything from simple browsing, YouTube, streaming TV/movies, to gaming. For games the most taxing is something like BG3, but I can't think of anything else in terms of taxing programmes.

I don't think I'd have a use for it if I kept it. Even if I kept the hard drive I'd have to research How and What To Save To Which Drive On Your PC, but if that's what y'all recommend then I can.

I'm not against investing a few grand if it's the right money spent at the right time, if that makes sense? My worry about changing individual parts is the standard worries about installation and compatibility, but if it's too soon to be changing the whole rig then I can get over that