My computer is getting slower and slower — how do I speed up Windows?

Free fixes first: disable unnecessary startup programs (Task Manager > Startup tab), run Disk Cleanup, and scan for malware. If it's still sluggish, the single biggest real-world improvement for an old machine is swapping a mechanical hard drive for an SSD — it's a night-and-day difference in boot and load times, usually more impactful than adding RAM.