The first software I would download and and run is ..
https://www.malwarebytes.com/mwb-download/
Make sure you download the
FREE version for Windows for Home .. it's all you need to check your computer for malware and remove it if found.
That will help you figure out if you have malware installed on your computer slowing it down.
You don't need to "buy" software to speed up your computer.
You simply need to figure out 1) what software is causing it to slow down or 2) where your computer is bottle-necking on resources.
The first thing you should do is open Task Manager. You can right-click the task bar to run it or use CTRL-SHIFT-ESC as a hotkey for it.
If you are running Windows 10 and the task manager window is small, click the "More Details" link and it will show you the full task manager.
Once you have that, click each of the columns starting with CPU sorting each one from largest-to-smallest (should show down arrow below column heading).
That should help you find if there are demanding processes running on your system that are causing it to slow down.
Your computer typically runs slow for one of three reasons ..
1) Performance-heavy software or Windows system (Search Indexing, Windows Update, etc.) processes are running in the background
2) Your hardware resources in the computer are too low (not enough memory, not enough drive space, slow hard drives, slow CPU, etc.)
3) Your computer is infected with malware
Use Malware Bytes Free version to eliminate #3.
The task manager should help you find issues with #1.
You will need tech help for #2 unless you are tech savvy.